220-1101 Power Supply — 20 Questions

Question 1

A technician is troubleshooting a PC that emits a high-pitched whining noise under load. The noise is coming from the power supply area. The system is stable and temperatures are normal. What is the most likely cause?

Accepted Answer

The PSU is experiencing coil whine due to electrical resonance.. Coil whine is a common phenomenon in power supplies and other components when electrical current passes through inductors, causing them to vibrate at audible frequencies. It is typically harmless and does not indicate a defect, though it can be annoying. If the system is stable, no replacement is needed.

Answer

The PSU fan bearing is failing.

Answer

The PSU is overheating and the thermal protection is activating.

Answer

The PSU has a loose internal component rattling.

Question 2

A technician is selecting a power supply for a workstation that will run 24/7 in a dusty environment. The PSU will be installed in a case with limited airflow. Which PSU feature is most important to prioritize for long-term reliability in this scenario?

Accepted Answer

A fan with a fluid dynamic bearing and a dust filter.. In dusty environments with limited airflow, a PSU with a high-quality, sealed bearing fan (e.g., fluid dynamic bearing) and a dust-resistant design (e.g., honeycomb grill, dust filters) is critical. Additionally, a higher efficiency rating (e.g., 80 Plus Gold or better) reduces heat output, easing thermal stress. The most important single feature is the fan's reliability and the PSU's ability to handle particulate ingress.

Answer

A high total wattage rating to ensure headroom.

Answer

A modular cable design for easier cable management.

Answer

An 80 Plus Bronze efficiency rating.

Question 3

A technician is replacing a power supply in an office desktop. The new PSU has a 24-pin main connector, but the motherboard has a 20-pin socket. What should the technician do?

Accepted Answer

Separate the detachable 4-pin section from the 24-pin connector and use the remaining 20-pin part.. Modern ATX power supplies often have a 24-pin connector that is backward compatible with 20-pin motherboards; the extra 4 pins can be slid or snapped off. This allows the PSU to work without modification. Forcing the 24-pin into a 20-pin socket could damage the board.

Answer

Use a 24-pin to 20-pin adapter.

Answer

Force the 24-pin connector into the 20-pin socket.

Answer

Return the PSU and buy one with a 20-pin connector.

Question 4

A technician is troubleshooting a PC that shuts down randomly after a few minutes of use. The technician measures the +12V rail with a multimeter and gets 11.2V. The +5V rail reads 4.9V, and the +3.3V rail reads 3.2V. What is the most likely diagnosis?

Accepted Answer

The power supply is failing and needs replacement.. The +12V rail is significantly below the ATX specification of ±5% (11.4V minimum), indicating a failing power supply. The other rails are within tolerance but the +12V is critical for CPU and GPU power. A failing PSU can cause random shutdowns as voltage drops under load. Replacement is necessary.

Answer

The motherboard voltage regulator is failing.

Answer

The system is drawing too much current, causing voltage drop.

Answer

The AC input voltage is too low.

Question 5

A technician is upgrading a server's power supply to support additional drives. The current PSU is a 750W unit with a single +12V rail rated at 62A. The new drives will add 5A to the +12V load. The total calculated +12V load is 58A. Is the current PSU adequate?

Accepted Answer

Yes, because 58A is less than 62A, so it is within specifications.. The PSU's +12V rail is rated for 62A, and the total load after adding drives is 58A, which is within the rating. However, it is good practice to leave headroom (typically 10-20%) to avoid running the PSU at maximum capacity, which can reduce efficiency and lifespan. In this case, the PSU is technically adequate but marginal.

Answer

No, because the PSU should not be loaded above 80% of its rating.

Answer

No, because the total wattage of 750W is insufficient for the new drives.

Answer

Yes, but only if the PSU is 80 Plus Gold certified or higher.

Question 6

A small business has several PCs that intermittently reboot or fail to start. The building's electrical system is old, and the technician suspects power quality issues. Which device should the technician recommend installing to protect the computers?

Accepted Answer

An uninterruptible power supply (UPS).. An uninterruptible power supply (UPS) provides battery backup and voltage regulation, protecting against surges, sags, and brownouts that can cause reboots or failures. A surge protector only guards against spikes, not low-voltage conditions. A UPS is the appropriate solution for unstable power.

Answer

A power strip with a surge protector.

Answer

A line conditioner (voltage regulator).

Answer

A dedicated circuit from the breaker panel.

Question 7

A technician is building a new workstation for video editing and needs to ensure the power supply can handle dual GPUs and multiple hard drives. Which specification is most critical to check when selecting a PSU?

Accepted Answer

The combined amperage on the +12V rail(s).. The +12V rail provides power to the CPU, GPUs, and drives; its combined amperage determines how much power can be delivered to these components. For high-power builds, a single +12V rail with high amperage or multiple rails with sufficient combined capacity is essential. Neglecting this can lead to instability or shutdowns under load.

Answer

The total wattage rating of the power supply.

Answer

The number of SATA power connectors.

Answer

The physical form factor (ATX, SFX, etc.).

Question 8

A technician is installing a new power supply in a high-end gaming PC. The PSU has two +12V rails rated at 20A each. The GPU requires a single +12V rail with at least 30A. What potential issue could arise?

Accepted Answer

The GPU may cause overcurrent protection to trip on one rail, causing shutdowns.. Multi-rail PSUs split the +12V output across separate rails, each with its own overcurrent protection. If the GPU draws more than 20A from one rail, it can trip the protection, causing shutdowns. Using a single-rail PSU or ensuring the GPU is connected across both rails (if the PSU allows) would avoid this.

Answer

The PSU will automatically combine the rails to provide 40A to the GPU.

Answer

The PSU will deliver stable power as long as the total wattage is sufficient.

Answer

The GPU will automatically draw power from both rails equally.

Question 9

A user reports that their computer does not power on at all. The technician verifies the power cord is connected and the wall outlet works. When the PSU is turned on, no fans spin and no LEDs light up. What should the technician check first?

Accepted Answer

Check if the power supply's on/off switch is set to the '1' (on) position.. The power supply switch is a simple but common oversight; if it is in the off (0) position, no power reaches the system. Always verify this before more complex troubleshooting. Other steps like testing the PSU with a multimeter or paperclip test come after confirming the switch is on.

Answer

Replace the CMOS battery.

Answer

Reseat the RAM modules.

Answer

Test the PSU with a multimeter.

Question 10

A customer reports that their desktop PC randomly shuts down when playing a graphically intensive game. The system has a 500W power supply, a high-end GPU, and a CPU with a 125W TDP. What is the most likely cause of the shutdowns?

Accepted Answer

The power supply is undersized for the system's peak power demands.. The random shutdowns under load suggest the power supply cannot deliver enough wattage to sustain peak power draw from the GPU and CPU. A 500W PSU may be insufficient for a high-end gaming system, causing voltage drops or thermal overload protection to trigger. Upgrading to a higher-wattage PSU with adequate +12V rail capacity would resolve the issue.

Answer

The GPU is overheating due to poor case airflow.

Answer

The motherboard's VRM is failing due to age.

Answer

The RAM is faulty causing memory errors during gaming.

Question 11

A technician is troubleshooting a PC that powers on for a few seconds then shuts off. The technician removes the 24-pin connector and jumps the green wire to a black wire; the PSU fan spins and stays on. What does this indicate?

Accepted Answer

The motherboard has a short circuit causing the PSU to shut down.. The paperclip test confirms the PSU can power on independently. If the fan runs continuously, the PSU is likely functional. The issue is probably elsewhere, such as a short on the motherboard or a faulty component drawing too much power.

Answer

The power supply is definitely faulty and should be replaced.

Answer

The CPU is overheating and triggering thermal shutdown.

Answer

The power supply fan is defective, causing it to overheat and shut off.

Question 12

A desktop PC fails to power on. The technician measures the voltage on the 24-pin motherboard connector and finds that the purple wire (5VSB) reads 4.9V, but the green wire (PS_ON) reads 0V when the power button is pressed. What does this indicate?

Accepted Answer

The motherboard is not sending the PS_ON signal, likely due to a fault.. The green wire (PS_ON) is pulled low by the motherboard to start the PSU. If it stays at 0V, the motherboard is not signaling the PSU to turn on. The 5VSB being present means the PSU's standby power is working, isolating the issue to the motherboard or front panel switch.

Answer

The power supply is faulty and needs replacement.

Answer

The power supply's +12V rail is shorted, causing overcurrent protection.

Answer

The front panel power switch is stuck in the closed position.

Question 13

A technician is installing a power supply in a new build. The case has a bottom-mounted PSU bay with a dust filter. The technician notices that the PSU fan faces downward. Is this correct?

Accepted Answer

Yes, the fan should face downward to draw cool air from outside the case.. In a bottom-mounted PSU configuration, the fan should face downward to draw cool air from outside the case through the dust filter. This improves cooling efficiency and reduces dust buildup inside the case.

Answer

No, the fan should face upward to exhaust hot air from inside the case.

Answer

No, the PSU should be mounted fan-up to prevent dust from entering.

Answer

The orientation does not matter as long as the PSU is securely mounted.

Question 14

A user reports that their computer emits a loud, high-pitched whine when under load, but is silent at idle. The system is stable. What is the most likely cause?

Accepted Answer

The power supply or GPU is experiencing coil whine due to electrical resonance.. Coil whine is a common phenomenon in power supplies and graphics cards when current flow causes inductor coils to vibrate at a frequency within human hearing. It is not a sign of failure unless accompanied by other symptoms.

Answer

The power supply fan bearing is failing, causing noise only when spinning faster.

Answer

The CPU cooler fan is unbalanced and vibrating against the case.

Answer

The hard drive is making noise as it reads data during gaming.

Question 15

A customer wants to install a modular power supply in their PC but notes that the included cables have different pin shapes on the PSU end. What should the technician advise?

Accepted Answer

The technician should use only the cables that came with that specific power supply.. Modular PSU cables are keyed to prevent incorrect insertion, but they are not standardized across brands. Using cables from a different PSU can cause shorts and damage components. Always use the cables that came with the specific PSU.

Answer

The cables are interchangeable as long as they fit the connector.

Answer

The technician should verify the pinout diagram and use cables from the same manufacturer.

Answer

The customer should return the PSU and buy a non-modular one.

Question 16

A technician is diagnosing a PC that will not power on. The multimeter shows 0V on all pins of the 24-pin connector when the PSU is plugged in and the power switch is on. What is the most likely cause?

Accepted Answer

The AC power cord is loose or the wall outlet is dead.. If no voltages are present, the PSU is not receiving AC power or its internal circuits are dead. The technician should check the AC outlet, power cord, and PSU switch first before concluding the PSU is faulty.

Answer

The motherboard is shorted, preventing the PSU from starting.

Answer

The power supply is completely dead and needs replacement.

Answer

The front panel power switch is faulty.

Question 17

A technician is replacing a power supply in a server that has been experiencing random lockups. The old PSU is an 80+ Bronze rated 650W unit. The technician selects an 80+ Gold rated 650W unit from the same brand. What is the primary benefit of this upgrade?

Accepted Answer

The Gold-rated PSU produces less heat and is more efficient.. 80+ Gold certification indicates higher efficiency (87-90% at typical loads) compared to Bronze (82-85%). This means less power is wasted as heat, which can improve reliability in a server environment and reduce cooling costs.

Answer

The Gold-rated PSU provides more wattage to the components.

Answer

The Gold-rated PSU has better voltage regulation and ripple suppression.

Answer

The Gold-rated PSU will automatically fix the random lockups.

Question 18

A customer reports that their desktop PC randomly shuts down when playing graphics-intensive games, but runs fine during web browsing. The power supply is a 450W unit. What is the most likely cause of the issue?

Accepted Answer

The power supply is underrated for the system's peak power draw.. This scenario tests understanding of power supply wattage requirements under load. Graphics-intensive gaming draws more power, and if the PSU cannot supply enough sustained wattage, the system may shut down to protect itself. A 450W unit is often insufficient for a gaming GPU, especially if the system has multiple drives or high-end components.

Answer

The CPU thermal paste has dried out, causing overheating only during gaming.

Answer

The graphics card driver is corrupted, causing system instability.

Answer

The motherboard capacitors are failing, causing intermittent power loss.

Question 19

A technician is upgrading a workstation by adding a second high-end GPU. The current power supply has a single +12V rail rated at 40A and two 6+2 pin PCIe power cables. What is the most important factor to check before proceeding?

Accepted Answer

The total power draw of the system does not exceed the PSU's +12V rail capacity.. The +12V rail's current rating determines how much power it can deliver to GPUs and CPU. A single rail at 40A provides 480W, which may be insufficient for two high-end GPUs. The technician must verify total system power draw against the PSU's capacity.

Answer

Whether the motherboard has enough SATA power connectors.

Answer

The physical clearance inside the case for the second GPU.

Answer

The operating system supports dual GPUs.

Question 20

A technician is building a new PC for a video editing workstation. The selected components include an Intel i9-13900K, an NVIDIA RTX 4080, 64GB DDR5 RAM, three NVMe SSDs, and six case fans. What is the minimum recommended power supply wattage for this build?

Accepted Answer

1000W. High-end CPUs and GPUs like the i9-13900K and RTX 4080 can draw over 300W each under load, plus other components. A 1000W PSU provides sufficient headroom for peak power spikes and ensures stability during intensive tasks.

Answer

750W

Answer

850W

Answer

1200W