What does the PC power supply actually do?
The PSU converts incoming mains electricity into the regulated DC power used by the motherboard, processor, storage, graphics card, fans and other components. That means a power problem can affect the whole computer, not only the power button.
Dell's desktop PSU troubleshooting guidance notes two broad failure patterns: a power supply may provide no power at all, or it may fail to provide sufficient voltage and current to the system. In practice, this is why one faulty PSU can produce a dead machine while another system still turns on but becomes unstable when demand increases.
Signs that can justify checking the power supply
| Symptom | Why the PSU is considered | Other faults to rule out |
|---|---|---|
| No lights, fans or response | No output or failed mains/power path | Wall socket, cable, switch, front-panel button, motherboard |
| PC starts then instantly stops | Protection may be tripping or output may collapse | Short circuit, motherboard, CPU power, incorrect cabling |
| Restarts during gaming or rendering | Higher GPU/CPU demand can expose an unstable supply | Overheating, GPU fault, RAM, driver or motherboard instability |
| Black screen or GPU drops under load | Graphics power delivery needs checking | GPU, display cable, driver, PCIe slot, overheating |
| Burning smell or melted connector | Electrical or connector failure may be present | Damaged cable, GPU socket or motherboard connector |
| PSU clicking or fan noise | Fan or protection behaviour may be abnormal | Normal relay click, case fan, hard drive, cable touching a fan |
A symptom is a starting point, not a part number. That distinction prevents unnecessary PSU replacement and reduces the risk of damaging a second component.
No power, no POST and no display are different faults
A desktop that appears dead needs to be classified correctly. Dell separates startup problems into no power, no POST, no boot and no video because each points the diagnosis in a different direction.
- No power: no meaningful lights, fans or activity. Check mains power, cable, PSU and board power path.
- No POST: the PC powers but never completes its hardware startup checks. Memory, CPU, motherboard, graphics and firmware can all be involved.
- No boot: POST completes but Windows does not load. The PSU may be fine; storage or Windows is more likely.
- No video: the system appears to run but the monitor has no image. Follow the display path before blaming the PSU.
If your machine powers up but the monitor says No Signal, use our PC turns on but no display guide before assuming the power supply has failed.
Safe checks before replacing a PSU
- Test a known-working wall outlet. Bypass a questionable extension lead or surge strip for the test.
- Check the mains lead. Reseat it at both ends and substitute a known-good compatible lead where appropriate.
- Check the PSU's external switch. If the unit has an I/O rocker switch, make sure it has not been knocked to Off.
- Record lights, fan movement and diagnostic LEDs. These clues help distinguish no power from no POST.
- Inspect external and visible low-voltage connectors with the machine unplugged. Look for loose CPU/GPU power connectors, heat damage or a cable disturbed during an upgrade.
- Remove recently added external devices. A shorted peripheral or USB device can complicate diagnosis.
- Use manufacturer self-test features only when the model provides them. Some Dell desktops include a built-in PSU self-test; follow the exact model instructions.
Do not open the power-supply enclosure. Corsair's PSU safety guidance states that high voltages are present inside and there are no user-serviceable components. The same safety principle applies regardless of brand.
Why does a PC shut down only during gaming or heavy work?
A machine can sit at the Windows desktop for hours and still fail during a game, render or benchmark. Heavy CPU and GPU work raises power demand and temperature at the same time, so the test needs to separate both.
Useful evidence includes whether the shutdown is instant, whether Windows records a blue screen, whether GPU temperatures were normal, whether the problem follows a particular graphics workload and whether a known-good PSU changes the behaviour. A Windows Kernel-Power event by itself only tells you that the previous shutdown was unexpected; it does not prove the PSU caused it.
For gaming systems, also check graphics-card power connectors, PSU capacity and the exact cable arrangement. If the fault appears only under graphics load, our graphics card diagnosis and gaming PC repair pages explain the wider test path.
Does buzzing, clicking or coil whine mean the PSU is failing?
Not automatically. A single relay click when a system starts or stops can be normal. High-frequency electrical noise commonly described as coil whine can occur without the PSU being electrically defective. A worn PSU fan can also make mechanical noise while the power electronics remain functional.
What matters is the combination of symptoms. Noise becomes more concerning when it arrives with shutdowns, a burning smell, visible heat damage, fan seizure or unstable output. First confirm that the sound is actually from the PSU rather than a case fan, GPU fan or hard drive.
What matters when replacing a desktop power supply?
Buying a PSU by wattage alone is not enough. Check the case form factor, motherboard connectors, CPU power connector, graphics-card connectors, total system demand and cable compatibility. Small-form-factor and manufacturer-specific desktops may use proprietary dimensions or wiring.
With modular power supplies, never assume the detachable cables from an old PSU can be reused with a new one. Connector ends can physically fit while the pinout differs. Corsair explicitly instructs users to use manufacturer-supplied modular cables for the power supply.
If a modern graphics card or other upgrade is the reason for changing the PSU, compare the whole system rather than simply fitting the largest unit available. Our computer upgrades in Birmingham service can check compatibility before parts are ordered.
When the motherboard can mimic a PSU fault
A motherboard short, damaged VRM, failed connector or another component pulling a power rail down can make a healthy PSU appear dead. This is why swapping the PSU is not always the end of the diagnosis.
If a known-good compatible supply still produces no POST, unusual diagnostic LEDs or repeated protection shutdowns, the board and connected components need testing. See our motherboard repair and diagnosis page for the next stage.
How we approach desktop power faults in Birmingham
- Confirm the exact failure: no power, no POST, shutdown under load or intermittent start.
- Check the external mains path and visible connections.
- Inspect for heat damage, loose power connectors and recent hardware changes.
- Isolate unnecessary components where appropriate.
- Test with known-good compatible hardware or model-specific diagnostics.
- Check whether the motherboard, graphics card or another component is creating the same symptom.
- Quote the practical repair route before chargeable work begins.
PC Repair Guru provides desktop PC repair in Birmingham from an appointment-only Small Heath workshop. Bring the tower and tell us what happens when you press the power button, including any lights, fan movement, smells or shutdown pattern.
Frequently asked questions
Can a bad PSU make a PC restart randomly?
Yes. An unstable or overloaded power supply can cause shutdowns or restarts, but overheating, RAM, graphics, motherboard and Windows faults can produce similar symptoms. Test the failure pattern before replacing the PSU.
Does a spinning PSU fan prove the power supply is good?
No. Fan movement only shows that some power or fan control is present. It does not prove that every output remains within specification under load.
Should I open a PC power supply to inspect it?
No. Desktop power supplies can contain hazardous voltages and are not user-serviceable. Manufacturer safety guidance says not to open the PSU case.
Can a motherboard fault look like a bad PSU?
Yes. Shorts, failed voltage regulation, damaged connectors or other board faults can stop a system powering or completing POST even when the PSU is able to provide power.
Should I use modular cables from another PSU?
Do not assume modular PSU cables are interchangeable. Use the cables specified by the power-supply manufacturer for that exact unit or compatible series.
Can PC Repair Guru test a desktop power fault in Birmingham?
Yes. We can test the power path, connected components and failure pattern before recommending a PSU, motherboard or other repair route.