This chapter covers the three most common PSU connector types you must know for the CompTIA A+ 220-1101 exam: the 24-pin motherboard connector, PCIe power connectors for graphics cards, and SATA power connectors for drives. These connectors are fundamental to hardware installation, troubleshooting, and upgrade scenarios. Expect roughly 5-8% of the exam questions to involve power supply connectors, often in the context of selecting the correct PSU for a build or diagnosing a system that won't power on.
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Think of a computer's power supply unit (PSU) as a city's electrical substation that converts high-voltage transmission lines into usable household voltage. The 24-pin main connector is like the main breaker panel that distributes power to all the general circuits in a house—lights, outlets, appliances. It provides multiple voltage rails (e.g., +3.3V, +5V, +12V) just as a panel has different breakers for different areas. The PCIe power connectors (6-pin or 8-pin) are like dedicated high-amperage circuits for heavy appliances like an electric oven or clothes dryer—they supply extra +12V power directly to the graphics card, which demands high current. The SATA power connector is like a standard wall outlet for low-power devices such as lamps or phone chargers—it provides +3.3V, +5V, and +12V to drives and peripherals. Just as you wouldn't plug a dryer into a standard outlet (insufficient current), you cannot power a high-end GPU solely from the 24-pin connector; it needs dedicated PCIe cables. The city grid analogy helps understand that each connector type is designed for specific power demands and that mismatching can lead to component damage or fire.
What Are PSU Connectors and Why Do They Exist?
A Power Supply Unit (PSU) converts AC mains electricity into DC voltages used by computer components. The connectors are the physical interfaces that deliver these voltages safely. Each connector type is standardized to provide specific voltages and current capacities. The 24-pin main connector supplies the motherboard with +3.3V, +5V, and +12V rails, along with control signals like Power Good and PS_ON#. PCIe connectors provide additional +12V power to graphics cards, which can draw over 75W from the PCIe slot alone. SATA power connectors deliver +3.3V, +5V, and +12V to storage devices and other peripherals.
The 24-pin Motherboard Connector
The 24-pin ATX connector (sometimes called the main power connector) is the largest connector from the PSU. It evolved from the older 20-pin ATX standard, adding four extra pins for additional +12V, +3.3V, and ground connections to support higher power demands of modern motherboards. The connector is keyed so it fits only one way; forcing it can damage the pins. Pinout includes: - +3.3V (orange wires): Used for chipset, RAM, and some PCIe slots. - +5V (red wires): Powers legacy devices like older hard drives and USB ports. - +12V (yellow wires): Powers CPU, GPU (via slot), and fans. - -12V (blue wire): Rarely used, historically for serial ports. - +5VSB (purple wire): Standby voltage, always active when PSU is plugged in, powers wake-on-LAN and USB charging. - Power Good (gray wire): Signal from PSU to motherboard indicating all voltages are stable; motherboard starts CPU only after this signal is true. - PS_ON# (green wire): Motherboard pulls this low to turn on the PSU.
A missing 4-pin section (often detachable) can be left off for older 20-pin motherboards, but modern boards require all 24 pins. The connector delivers up to about 150W total, but most of that is on +12V (up to ~120W).
PCIe Power Connectors
PCIe power connectors are dedicated +12V connectors for graphics cards. They come in 6-pin (75W) and 8-pin (150W) variants. The 6-pin has three +12V pins and three ground pins; the 8-pin adds two more ground pins and one +12V pin, plus a sense pin that tells the GPU the connector is 8-pin. Some high-end cards use multiple connectors (e.g., two 8-pin for up to 375W total from PSU). The PCIe slot itself can provide up to 75W (for x16 slots), so a card with one 6-pin can draw up to 150W total. The connector is keyed differently from CPU EPS12V (which also supplies +12V) to prevent misconnection. However, some PSUs have cables that are physically identical but electrically different; always check labeling.
SATA Power Connector
The SATA power connector is a 15-pin L-shaped connector that supplies +3.3V, +5V, and +12V to SATA drives (HDDs, SSDs, optical drives). It also includes ground pins. Each voltage pin is rated for 1.5A, giving a maximum of 4.5W for +3.3V, 7.5W for +5V, and 18W for +12V per connector. In practice, drives draw much less; a typical 3.5" HDD uses about 5-10W. The connector is designed to be hot-swappable (though not all controllers support it). The +3.3V rail is used by some SSDs for power-disable (PWDIS) feature, which can cause issues if the PSU does not provide stable +3.3V.
Key Values and Defaults
24-pin connector: Maximum current per pin is about 6A for +12V, 5A for +5V, 3A for +3.3V.
PCIe 6-pin: 75W max (two +12V pins at 6A each? Actually, three +12V pins at 6A each = 18A * 12V = 216W, but the connector is rated for 75W due to thermal limits; the standard limits current to 8A per pin but derates for safety). The official PCI-SIG spec: 6-pin = 75W, 8-pin = 150W.
SATA power: Each voltage pin rated 1.5A, total 54W theoretical, but practical limit ~30W due to connector heating.
Power Good signal: Must assert within 100-500ms after power-on; if not, motherboard may not start.
+5VSB: Minimum 2A for modern systems, often 3A+ for USB charging.
How They Interact
The 24-pin provides base power to motherboard and slot-powered devices. The CPU gets its own dedicated 4+4 pin EPS12V connector (not covered in this chapter but related). PCIe connectors supplement graphics card power beyond the slot's 75W limit. SATA power is for drives and sometimes for fan hubs or RGB controllers via adapters. When building a system, the PSU must have enough connectors and wattage to support all components. For example, a high-end GPU may require two 8-pin PCIe connectors; if the PSU only has one, an adapter from two SATA or Molex can be used, but this risks overloading the SATA cables (SATA power is not rated for high GPU loads).
Configuration and Verification
There is no software configuration for these connectors; they are physical. However, you can verify voltages using a multimeter on the back of the connector (with system on) or via BIOS/UEFI sensor readings. Tools like HWMonitor show +12V, +5V, +3.3V rails. If voltages are out of spec (e.g., +12V below 11.4V or above 12.6V), the PSU may be failing. The Power Good signal can be checked with an oscilloscope or a PSU tester.
Common Issues
Loose connections cause intermittent power loss.
Using wrong cable (e.g., EPS12V into PCIe slot) can short circuit and destroy components.
Daisy-chaining PCIe power (using one cable with two connectors) for high-power GPUs can cause cable melting; use separate cables.
SATA power connectors on some PSUs have thin wires that cannot handle high current; avoid using SATA-to-PCIe adapters for GPUs over 75W.
Exam Relevance
The 220-1101 exam expects you to identify these connectors by sight (e.g., from an image), know their voltage outputs, and understand which component uses which connector. You must also know that the 24-pin can be split into 20+4 for older motherboards. PCIe 6-pin vs 8-pin: the 8-pin has an extra ground and a sense pin; the sense pin is key to distinguishing. SATA power is often confused with Molex; know that SATA is 15-pin, Molex is 4-pin. Also know that some modern GPUs use a new 12VHPWR connector (16-pin) but that is not in 220-1101 objectives.
Identify Power Requirements
Before connecting any PSU cables, determine the power needs of each component. Check the CPU power (usually an 8-pin EPS12V), motherboard main power (24-pin), GPU power (6-pin or 8-pin PCIe), and SATA devices. Use the component specifications to ensure the PSU has the correct cables and wattage. For example, a high-end GPU may require two 8-pin connectors; the PSU must have at least two dedicated PCIe cables (not daisy-chained). Failure to do this step can result in insufficient power delivery and system instability.
Connect 24-pin Motherboard Power
Align the 24-pin connector with the motherboard socket. The connector is keyed with a clip that snaps into place. Ensure the clip is fully engaged. If the motherboard has a 20-pin socket, the detachable 4-pin section can be left unconnected (some PSUs have a 20+4 pin design). Apply firm, even pressure until the clip locks. A loose connection can cause intermittent power loss or failure to boot. The Power Good signal will not assert if the connector is not fully seated.
Connect CPU Power (EPS12V)
Although not the main topic, the CPU power connector is closely related. Usually a 4+4 pin that can be used as 4-pin or 8-pin. This connector provides +12V directly to the CPU voltage regulator. It is physically similar to PCIe but keyed differently; do not force. Connect the correct cable labeled 'CPU' or 'EPS'. Using a PCIe cable here can cause a short and damage the motherboard. Ensure the clip engages. The CPU power is critical; without it, the system may power on but not post.
Connect PCIe Power to GPU
Identify the PCIe power cables from the PSU; they are usually labeled 'PCIe' or have a 6+2 pin design that can be used as 6-pin or 8-pin. Insert the connector into the graphics card's power socket until the clip locks. For cards with multiple sockets, use separate cables from the PSU for each socket rather than daisy-chaining from one cable. This ensures each cable carries only its rated current. A single 8-pin cable can safely deliver 150W; two cables can deliver 300W. Using a daisy-chain cable for a 300W GPU can exceed the cable's rating and cause overheating or fire.
Connect SATA Power to Drives
Use SATA power cables from the PSU. These are the L-shaped 15-pin connectors. Align the connector with the drive's power port and push gently until it clicks. SATA power is keyed, so it cannot be inserted upside down. Some PSUs have multiple SATA connectors on a single cable; this is fine for drives as each drive draws low power (typically under 10W). However, avoid using SATA-to-PCIe adapters for GPUs because SATA cables are not rated for high current draw (max 1.5A per pin, total ~54W), and a GPU can draw 150W, causing the cable to melt.
Enterprise Workstation Build
A company orders high-end workstations for CAD rendering. Each workstation has an Intel Core i9-13900K (125W TDP), an NVIDIA RTX 4090 (450W TDP), 64GB RAM, multiple NVMe SSDs, and a 1000W PSU. The PSU must have at least four 6+2 pin PCIe connectors (the RTX 4090 uses a 12VHPWR adapter that requires four 8-pin connectors). The technician uses separate PCIe cables for each connector to avoid overloading any single cable. The 24-pin main power is connected, and the CPU power uses two 8-pin EPS12V connectors. The SATA power is used only for a couple of 2.5" SSDs. The system boots and runs stress tests without issues. Common mistake: using a daisy-chain cable for two of the GPU connectors, leading to voltage drop and instability under load. The technician ensures each cable is dedicated.
Data Center Server Deployment
In a data center, servers use redundant power supplies (2+1 configuration). Each PSU has a 24-pin main connector and multiple CPU power connectors. However, many servers use proprietary connectors for the backplane. In a typical 1U server, the PSU connects to a power distribution board that distributes power to the motherboard and drives via custom connectors. The 24-pin standard is still present but often in a different form factor (e.g., right-angle connector). SATA power is used for hot-swap drive bays. A common issue is a loose connection on the 24-pin causing intermittent server crashes. Technicians use PSU testers to verify voltage rails before installation.
Home Gaming PC Upgrade
A gamer upgrades from a GTX 1060 (120W) to an RTX 3080 (320W). The existing 500W PSU has only one 6+2 pin PCIe cable. The RTX 3080 requires two 8-pin connectors. The gamer tries using a SATA-to-PCIe adapter to get a second 8-pin. During gaming, the SATA cable overheats and melts, causing a short. The correct solution is to upgrade to a PSU with sufficient PCIe connectors (e.g., 750W with two dedicated PCIe cables). This scenario highlights the importance of matching connector types to power requirements and never using adapters that exceed the cable's rating.
What the 220-1101 Tests
Objective 3.5 (Given a scenario, install and configure power supplies and cooling) includes identifying and connecting PSU connectors. The exam expects you to:
Recognize the 24-pin motherboard connector, PCIe (6-pin and 8-pin), and SATA power by sight.
Know the voltage outputs: 24-pin provides +3.3V, +5V, +12V, -12V, +5VSB. PCIe provides +12V only. SATA provides +3.3V, +5V, +12V.
Understand the power capacity: PCIe slot provides 75W; 6-pin adds 75W; 8-pin adds 150W. SATA power is limited (drives draw less than 10W).
Know that the 24-pin can be split into 20+4 for older motherboards.
Be aware that PCIe and EPS12V connectors are physically different and not interchangeable.
Common Wrong Answers
Confusing PCIe 6-pin with EPS12V 8-pin: Both supply +12V, but EPS12V has a different keying. The exam may show an image of a 4+4 pin (EPS) and ask which component it powers; many choose GPU incorrectly.
Believing the 24-pin connector powers the CPU: The CPU has its own dedicated connector. The 24-pin supplies the motherboard, which then powers the CPU via the VRM, but the high-current CPU power comes from EPS12V.
Assuming SATA power can be used for GPUs: Some candidates think a SATA-to-PCIe adapter is safe. The exam expects you to know SATA power is only for low-power devices.
Mixing up +5VSB and Power Good: +5VSB is always on; Power Good is a signal that goes high after voltages stabilize. A question might describe a system that powers on but doesn't boot; candidates might suspect +5VSB but the correct issue is Power Good.
Numbers and Terms That Appear Verbatim
"24-pin ATX main power connector"
"6-pin PCIe power connector (75W)"
"8-pin PCIe power connector (150W)"
"SATA 15-pin power connector"
"+12V rail"
"Power Good signal"
"+5VSB (standby)"
Edge Cases
Some motherboards have a 10-pin or 18-pin main power (proprietary); the exam focuses on standard ATX.
The 24-pin connector may have a 4-pin detachable section; the exam may show a 20-pin motherboard and ask which part to leave off.
Some PSUs have a 6+2 pin PCIe connector that can be used as 6 or 8; the exam tests that the 8-pin includes a sense pin.
How to Eliminate Wrong Answers
If a component needs more than 75W, it cannot rely solely on the slot; it needs PCIe power.
If a question shows a connector with 15 pins in an L-shape, it is SATA power.
If a question shows a connector with 24 pins in a rectangular shape, it is the main motherboard power.
For GPU power, look for 6 or 8 pins with a clip orientation that matches PCIe (not EPS).
The 24-pin motherboard connector provides +3.3V, +5V, +12V, -12V, +5VSB, and Power Good signal.
PCIe 6-pin power connector is rated for 75W; 8-pin is rated for 150W. Both supply only +12V.
SATA power connector is 15-pin and provides +3.3V, +5V, and +12V; rated for 1.5A per pin.
The 24-pin connector can be split into 20+4 for compatibility with older motherboards.
PCIe and EPS12V connectors are not interchangeable; using the wrong one can cause damage.
Never use SATA-to-PCIe adapters for GPUs drawing more than 75W; SATA cables are not rated for high current.
The Power Good signal must assert within 100-500ms for the system to boot; +5VSB is always on.
A graphics card may draw up to 75W from the PCIe slot; additional power requires PCIe cables.
When using multiple PCIe connectors on a GPU, use separate cables from the PSU to avoid overloading a single cable.
Always match the PSU connector to the component's power requirements; check the PSU's label for available connectors.
These come up on the exam all the time. Here's how to tell them apart.
24-pin Motherboard Connector
Provides +3.3V, +5V, +12V, -12V, +5VSB, and Power Good signal.
Rated for up to ~150W total, with most current on +12V.
Connects to motherboard main power socket; keyed with a clip.
Can be split into 20+4 for older motherboards.
Always required for any system; without it, system will not power on.
PCIe Power Connector (8-pin)
Provides only +12V (three +12V pins, five ground pins, one sense pin).
Rated for 150W (6-pin 75W).
Connects to graphics card; keyed differently from EPS12V.
Often comes as 6+2 pin to support both 6 and 8-pin sockets.
Required only if GPU power exceeds 75W from slot.
PCIe 6-pin Connector
Has three +12V pins and three ground pins.
Rated for 75W maximum.
No sense pin; GPU detects 6-pin by absence of sense pin.
Physically smaller than 8-pin.
Can be used on an 8-pin socket with a 6+2 adapter (but limited to 75W).
PCIe 8-pin Connector
Has three +12V pins, five ground pins, and one sense pin.
Rated for 150W maximum.
Sense pin tells GPU that 8-pin is connected, allowing higher power draw.
Often used for high-end GPUs requiring >150W.
Can be split as 6+2 for compatibility with 6-pin sockets.
SATA Power Connector
15 pins, L-shaped, keyed.
Provides +3.3V, +5V, +12V.
Rated for 1.5A per pin, total ~54W theoretical.
Used for modern SATA drives (HDDs, SSDs, optical).
Supports hot-swapping (with controller support).
Molex (4-pin) Connector
4 pins, round, keyed with beveled edges.
Provides +5V and +12V only (no +3.3V).
Rated for higher current per pin (up to 11A per pin, but typically 5A), total ~60W.
Used for older drives, fans, and some peripherals.
Not designed for hot-swapping.
Mistake
The 24-pin connector provides power to the CPU directly.
Correct
The 24-pin provides power to the motherboard chipset, RAM, and slots. The CPU receives power from a dedicated 4+4 pin EPS12V connector (or 8-pin). The 24-pin does supply some +12V to the motherboard, but the CPU's high current draw requires its own connector.
Mistake
A PCIe 6-pin connector can safely power a 150W GPU if used with an adapter.
Correct
A single 6-pin is rated for 75W. Using an adapter to combine two 6-pin into one 8-pin does not increase the current capacity of the cable; it still draws 150W through the same wires, risking overheating. Always use a native 8-pin cable or two separate 6-pin cables from the PSU.
Mistake
SATA power connectors are interchangeable with Molex connectors.
Correct
SATA power is 15-pin and supplies +3.3V, +5V, +12V. Molex is 4-pin and supplies +5V and +12V only. They are not interchangeable without an adapter, and the +3.3V rail is critical for some SSDs' power-disable feature.
Mistake
The Power Good signal is the same as +5VSB.
Correct
+5VSB (standby) is always on when the PSU is plugged in, even when the computer is off. Power Good (gray wire) is a signal that goes high only after all voltages are stable (within 100-500ms of power-on). The motherboard uses Power Good to reset the CPU; without it, the system may not boot.
Mistake
You can use any 8-pin connector for a GPU as long as it fits.
Correct
There are two types of 8-pin connectors: PCIe (6+2) and EPS12V (4+4). They are keyed differently to prevent cross-connection, but some PSUs have universal cables that can fit both. Using an EPS12V cable in a GPU can cause a short because the pinout is different (EPS has two +12V and two ground on one half; PCIe has three +12V and five ground). Always use cables labeled for the component.
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A 6-pin PCIe connector delivers up to 75W, while an 8-pin delivers up to 150W. The 8-pin has two additional ground pins and a sense pin that tells the GPU it can draw more power. Many PSUs provide a 6+2 pin cable that can be used as either. Always use the appropriate connector for your GPU's requirements; using a 6-pin on an 8-pin socket may limit power and cause instability.
No, you should not. SATA power cables are rated for low current (1.5A per pin, total ~54W), while a graphics card can draw 150W or more. Using a SATA-to-PCIe adapter can overload the SATA cable, causing it to overheat and potentially melt or cause a fire. Always use dedicated PCIe power cables from the PSU.
The Power Good (PWR_OK) signal is a +5V signal from the PSU to the motherboard that indicates all output voltages are within specification and stable. The motherboard uses this signal to reset the CPU and start the boot process. If the signal does not assert within 100-500ms after power-on, the system may not boot. A failing PSU may not assert Power Good, causing a no-post condition.
The 24-pin connector can supply up to about 150W total, distributed across the +3.3V, +5V, and +12V rails. The +12V rail is the most heavily used, providing up to ~120W. However, modern motherboards draw less than 100W typically, with the CPU and GPU getting power from dedicated connectors.
Both supply +12V, but they have different pinouts and keying. EPS12V (4+4 pin) is used for CPU power and has two +12V pins and two ground pins per 4-pin section. PCIe 8-pin (6+2) has three +12V pins, five ground pins, and a sense pin. They are physically shaped differently to prevent cross-connection; forcing them can damage components.
No, not directly. A 20-pin PSU lacks the extra +12V, +3.3V, and ground pins needed for modern motherboards. However, some 20-pin PSUs have a detachable 4-pin that can be added, but that is actually a 20+4 pin design. If you have a true 20-pin PSU, you need an adapter or a new PSU. The motherboard may not receive enough power, causing instability.
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