Power Supply practice questions

The PSU fan bearing is failing.

Why wrong: A failing fan bearing would produce a grinding or rattling noise, not a high-pitched whine, and would likely be intermittent or constant, not load-dependent.

The PSU is overheating and the thermal protection is activating.

Why wrong: Overheating would trigger fan speed increases or shutdowns, not produce a high-pitched whine; temperatures are reported as normal.

The PSU has a loose internal component rattling.

Why wrong: A loose component would cause a rattling sound, not a consistent high-pitched whine, and would likely be present at all times.

A high total wattage rating to ensure headroom.

Why wrong: Wattage headroom is useful but does not address the environmental challenges of dust and limited airflow; a high-wattage PSU may still fail if its fan clogs or overheats.

A modular cable design for easier cable management.

Why wrong: Modular cables improve airflow inside the case but do not protect the PSU itself from dust ingress or fan failure.

An 80 Plus Bronze efficiency rating.

Why wrong: While Bronze is decent, a higher efficiency rating (Gold or Platinum) would reduce heat output, which is beneficial in limited airflow, but the fan and dust protection are more critical for long-term reliability in dusty environments.

Use a 24-pin to 20-pin adapter.

Why wrong: An adapter is unnecessary because the 24-pin connector is designed to separate into a 20-pin and a 4-pin section; using an adapter adds an extra point of failure.

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

Why wrong: Forcing the connector can bend pins or damage the motherboard socket; the connector should never be forced.

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

Why wrong: This is unnecessary and time-consuming; the 24-pin PSU is fully compatible with the 20-pin motherboard as designed.

The motherboard voltage regulator is failing.

Why wrong: A failing VRM would typically cause instability on the CPU or memory, but the low +12V reading is measured at the PSU output, indicating the source is the PSU itself.

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

Why wrong: While excessive load can cause voltage drop, the PSU should still regulate within spec if it is functioning correctly; a healthy PSU would shut down or limit current before dropping this low.

The AC input voltage is too low.

Why wrong: Low AC input would affect all rails proportionally, but the +5V and +3.3V rails are within spec, so the issue is isolated to the +12V rail regulation.

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

Why wrong: While 80% is a recommended guideline for efficiency and longevity, it is not a hard limit; the PSU can operate at 93% load (58/62) without immediate failure, but it is not optimal.

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

Why wrong: The additional drives add 5A at 12V, which is 60W; total wattage is still well under 750W, so wattage is not the issue.

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

Why wrong: Efficiency certification does not affect the PSU's ability to deliver rated current; it only indicates how much power is wasted as heat.

A power strip with a surge protector.

Why wrong: A surge protector only protects against voltage spikes, not sags or brownouts, which are likely causing the intermittent reboots.

A line conditioner (voltage regulator).

Why wrong: A line conditioner stabilizes voltage but does not provide battery backup; if power drops out completely, the PC will still shut down.

A dedicated circuit from the breaker panel.

Why wrong: A dedicated circuit reduces interference from other devices but does not protect against utility-side power quality issues like sags or brownouts.

The total wattage rating of the power supply.

Why wrong: Total wattage is important but does not guarantee adequate +12V rail capacity; some PSUs have low +12V output relative to their total rating, which can still cause issues.

The number of SATA power connectors.

Why wrong: While multiple drives require SATA connectors, the most critical factor is ensuring the PSU can deliver enough power to the GPUs and CPU, which use the +12V rail.

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

Why wrong: Form factor determines fit in the case, not power delivery capability; it is important but secondary to the electrical specifications.

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

Why wrong: Multi-rail PSUs do not automatically combine rails; each rail is independent and limited to its rated amperage. Combining requires specific PSU design or configuration.

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

Why wrong: Total wattage is not the only factor; rail current limits matter. Even if total wattage is adequate, exceeding a single rail's limit can cause problems.

The GPU will automatically draw power from both rails equally.

Why wrong: The GPU does not manage rail distribution; it draws power from the connectors it is plugged into. If both connectors are on the same rail, the load is not balanced.

Replace the CMOS battery.

Why wrong: A dead CMOS battery prevents BIOS settings from being saved but does not stop the system from powering on; fans and LEDs would still activate.

Reseat the RAM modules.

Why wrong: RAM issues cause beep codes or no display but do not prevent the PSU from powering on; fans would still spin.

Test the PSU with a multimeter.

Why wrong: Using a multimeter is a valid diagnostic step but should be performed after ruling out simpler causes like the switch position.

The GPU is overheating due to poor case airflow.

Why wrong: While overheating can cause shutdowns, the scenario describes random shutdowns during gaming, which is more consistent with power supply insufficiency; thermal issues would typically cause gradual performance throttling or a specific temperature warning.

The motherboard's VRM is failing due to age.

Why wrong: VRM failure is less common and would likely cause instability at all times, not just under gaming load, and would not be resolved by a PSU upgrade.

The RAM is faulty causing memory errors during gaming.

Why wrong: Faulty RAM typically causes blue screens, application crashes, or boot failures, not random shutdowns without error messages.

The power supply is definitely faulty and should be replaced.

Why wrong: The PSU passed the paperclip test, so it is not faulty. The problem lies elsewhere in the system.

The CPU is overheating and triggering thermal shutdown.

Why wrong: Thermal shutdown takes longer than a few seconds; the immediate shutdown points to an electrical fault.

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

Why wrong: The fan spun during the test, so it is not defective. Also, overheating would not cause immediate shutdown.

The power supply is faulty and needs replacement.

Why wrong: A faulty PSU would typically show no 5VSB or incorrect voltages on other rails. Here, 5VSB is good, so the PSU is likely functional.

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

Why wrong: A short would cause the PSU to shut down immediately, but PS_ON would still be pulled low briefly. The 0V reading indicates no signal.

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

Why wrong: A stuck switch would continuously pull PS_ON low, not keep it at 0V. The reading shows the switch is not making contact.

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

Why wrong: Facing upward would pull hot air from inside the case into the PSU, reducing its cooling efficiency and lifespan.

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

Why wrong: Fan-up orientation would pull dust from inside the case into the PSU, and the dust filter would be ineffective.

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

Why wrong: Orientation significantly affects thermal performance and dust accumulation; it should always follow case design guidelines.

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

Why wrong: A failing fan would produce a grinding or rattling noise, not a high-pitched whine. Fan noise is mechanical, not electrical.

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

Why wrong: Unbalanced fans cause low-frequency vibration or rattling, not a high-pitched whine.

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

Why wrong: Hard drives produce clicking or whirring sounds, not a consistent high-pitched whine that changes with load.

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

Why wrong: Pinouts vary between PSU brands; using mismatched cables can deliver wrong voltages and destroy hardware.

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

Why wrong: Even same-brand cables may differ between models; it is safest to use only the cables included with the PSU.

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

Why wrong: This is unnecessary; modular PSUs are fine as long as the correct cables are used.

The motherboard is shorted, preventing the PSU from starting.

Why wrong: A shorted motherboard would cause the PSU to shut down after starting, not show 0V on all pins; the PSU would still produce standby voltage briefly.

The power supply is completely dead and needs replacement.

Why wrong: While possible, the technician should first verify AC power input; a dead PSU is not the only explanation.

The front panel power switch is faulty.

Why wrong: A faulty switch would prevent the PSU from turning on, but the PSU would still have standby voltage (5VSB) present. Here, there is no voltage at all.

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

Why wrong: Both are 650W units; efficiency rating does not affect maximum output wattage.

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

Why wrong: While Gold units often have better components, efficiency rating alone does not guarantee superior voltage regulation; that depends on design.

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

Why wrong: Lockups could be caused by many factors; a PSU upgrade may help if the old unit was failing, but efficiency does not directly fix stability.

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

Why wrong: While overheating can cause shutdowns, the symptom is specific to power draw under load, not thermal throttling. The scenario does not mention high temperatures.

The graphics card driver is corrupted, causing system instability.

Why wrong: Driver issues typically cause crashes or artifacts, not random shutdowns specifically tied to power load.

The motherboard capacitors are failing, causing intermittent power loss.

Why wrong: Bad capacitors can cause instability, but the pattern—only under gaming load—points to PSU capacity, not motherboard failure.

Whether the motherboard has enough SATA power connectors.

Why wrong: SATA connectors are for storage drives, not GPUs. The upgrade requires PCIe power cables, not SATA.

The physical clearance inside the case for the second GPU.

Why wrong: While physical fit is important, the electrical power delivery is the primary concern; a PSU that cannot supply enough current will cause instability.

The operating system supports dual GPUs.

Why wrong: OS support is secondary; if the PSU cannot deliver power, the system won't run regardless of software support.

750W

Why wrong: 750W may be borderline for this configuration; peak power spikes could exceed capacity, causing shutdowns or instability.

850W

Why wrong: 850W might work but leaves little headroom for transient spikes, which can trigger overcurrent protection on some PSUs.

1200W

Why wrong: 1200W is more than necessary and adds cost without benefit for this configuration, though it would work.