How to Tell If Your PC Power Supply Is Starting to Fail

TL;DR: A failing power supply usually shows up as random shutdowns under load, random reboots, burning smells, coil whine, or a system that won't POST at all. Most of these symptoms overlap with bad RAM or a failing motherboard, so the fix is to isolate the PSU with a controlled test before replacing anything. Here's the sequence that avoids guesswork.

What you need

1. A multimeter (optional but useful for voltage checks)
2. A paperclip or jumper wire (for the paperclip test)
3. Access to the PSU label for wattage and rail specs
4. A spare, known-good power supply if you have one, or access to a shop that can bench test
5. Basic antistatic precautions (unplug the PC, touch a grounded metal surface before opening the case)

If any of this involves opening a desktop tower you're not comfortable cracking open, skip to the diagnostic steps you can do without tools, then bring the machine in rather than swapping parts on a guess.

Step 1: Know the symptoms that actually point to the PSU

Power supplies fail in a few predictable ways. Not every weird PC behavior is a PSU problem, so start by matching what you're seeing against this list.

1. Random shutdowns under load. The PC powers off completely during gaming, rendering, or other high-draw tasks, then boots back up fine. This is the classic symptom of a PSU that can't sustain its rated output anymore.
2. Random reboots, not shutdowns. Less common for PSU issues specifically, but worth ruling in if it happens alongside load spikes.
3. No power at all. No fans spin, no lights, nothing on the motherboard. Could be the PSU, could be the outlet, could be the power switch on the PSU itself (check that first, it's an easy miss).
4. Burning smell or visible scorching near the PSU exhaust vent. This is a stop-use situation. Don't keep powering the machine on to see what happens.
5. Coil whine or a high-pitched buzz that changes with load. Some of this is normal on certain units, but a new or worsening whine is worth noting.
6. Failed POST with no clear cause, meaning you've already ruled out RAM reseating and a cleared CMOS and it still won't start.
7. Capacitor bulging or leakage visible on the PSU's circuit board if you remove the cover (only do this if you're comfortable and the unit is unplugged and discharged).

Step 2: Rule out the obvious before blaming the PSU

1. Check the wall outlet with another device, a lamp or phone charger works.
2. Confirm the PSU's rear power switch is in the "on" position (the 0/I rocker switch).
3. Reseat the 24-pin motherboard connector and the 4/8-pin CPU power connector. These vibrate loose more than people expect.
4. Try a different outlet and a different power cable if you have a spare.
5. If you have a surge protector or UPS in the chain, bypass it temporarily to rule it out as the fault.

These five checks take ten minutes and eliminate a surprising number of false PSU alarms.

Step 3: Run the paperclip test to confirm the PSU powers on

This test tells you whether the PSU turns on and spins its fan, not whether it's actually delivering clean, stable power. Still, it's a fast first filter.

1. Unplug the PSU from the wall and disconnect the 24-pin cable from the motherboard.
2. On the 24-pin connector, find the green wire (PS_ON) and any black wire (ground).
3. Insert a paperclip or jumper wire bridging those two pins.
4. Plug the PSU back into the wall and flip the rear switch on.
5. The PSU fan should spin up immediately. If it doesn't spin at all, that's a strong sign the unit is dead. If it spins but the PC still won't boot once reconnected, the PSU may be providing power but not enough, or not clean enough, under real load.

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Step 4: Check voltages with a multimeter if you have one

1. With the paperclip test running, probe the 24-pin connector pins with a multimeter set to DC volts.
2. The +12V rail should read close to 12V (within roughly 5 percent, so 11.4 to 12.6V).
3. The +5V rail should read close to 5V, and +3.3V close to 3.3V.
4. Rails that sag well outside those ranges, especially under any load, point to a PSU that's degrading even if it technically powers on.

This step is optional. Most home users skip it and go straight to a swap test, which is just as conclusive.

Step 5: Swap test with a known-good PSU

This is the most reliable DIY diagnostic. If you have access to a second power supply of adequate wattage:

1. Power down and unplug the system completely.
2. Swap in the known-good PSU, connecting the same cables to the same components.
3. Boot the system and run it through the same workload that triggered the original symptom (a game, a render, whatever caused the shutdown).
4. If the problem disappears, the original PSU is confirmed as the cause.
5. If the problem persists, the fault is elsewhere, likely RAM, the motherboard, or an overheating CPU, and you've just saved yourself from replacing a part that wasn't broken.

If you don't own a spare PSU, this is exactly the kind of test a repair shop can run on a bench in a few minutes with known-good hardware, which is faster and more conclusive than buying a new PSU on a hunch.

Common mistakes

1. Blaming the PSU for every random shutdown. Overheating CPUs and failing motherboard VRMs cause similar symptoms. Isolate before you buy.
2. Ignoring wattage headroom when replacing. A failing PSU under genuine overload needs a higher-wattage unit, not an identical replacement that will fail the same way.
3. Continuing to use a unit that smells burnt. That's a fire risk, not a "monitor it and see" situation.
4. Skipping the cheap checks. A loose 24-pin connector or a flipped rear switch looks identical to PSU failure until you check it.
5. Buying a cheap replacement PSU. A bargain unit with no real protection circuitry can damage other components if it fails again. This is the one place where spending a bit more is genuinely preventable risk management.
6. Opening a laptop to check the power supply. Laptops don't have a discrete PSU in the same sense, the issue is almost always the charger, the DC jack, or the battery. That's a different diagnostic path.

Bottom line

A failing power supply announces itself through load-triggered shutdowns, smells, whine, or a no-boot condition, but all of those overlap with other hardware faults. Run the elimination steps in order rather than replacing parts by guess. If you've gotten through the paperclip and swap tests and still aren't sure, or you don't have spare hardware to test with, bring it to a shop that can bench test the PSU against known-good components. See computer repair for diagnostic and replacement work, or schedule a repair if you'd rather skip the troubleshooting and have it confirmed properly. If the machine won't power on at all and you're not local to West Palm Beach, remote support can at least help rule out software and BIOS causes before you open the case.

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