Check your power supply before you assume it's broken
A failing power supply often looks like a random computer crash, a sudden shutdown, or a PC that won't start at all. Before you replace it, you can run several tests from inside Windows to see whether the power supply is actually the problem. Most of these checks take five minutes and require no tools or technical knowledge.
The simplest approach is to listen and watch: a power supply that's dying usually makes noise, the PC shuts down under load, or Windows reports power-related errors in its system logs. If none of those signs appear, your power supply is probably fine. If they do, the tests below will help you narrow down whether the power supply itself is failing or whether something else is drawing too much power.
Key Takeaways
- A power supply under stress often causes random shutdowns, especially when you're gaming or running heavy programs.
- Windows Event Viewer logs power events automatically, and you can check these logs without installing anything.
- Stress-testing software like Prime95 or MemTest86 pushes your power supply to its limit and reveals failures that normal use won't trigger.
- A power supply's age and the total wattage of your components both matter — a 10-year-old 500W supply powering a high-end graphics card is more likely to fail.
- If tests show no errors but your PC still crashes under load, the power supply may be failing intermittently, and replacement is the safest next step.
Check Windows Event Viewer for power-related errors
Windows automatically logs every unexpected shutdown and power event. Event Viewer is built into Windows and shows you these logs without installing anything. Open Event Viewer by typing "Event Viewer" into the Windows search box and pressing Enter.
Once Event Viewer opens, click on "Windows Logs" in the left panel, then click "System". You'll see a long list of events. Look for entries labeled "Critical" or "Error" that mention "power", "shutdown", or "kernel-power". Kernel-power errors (event ID 41) are the most telling — they mean Windows shut down without warning, which often points to a power supply that cut out suddenly.
If you see several kernel-power errors clustered around the times your PC crashed, that's a strong sign the power supply is failing. If Event Viewer is empty or shows only routine maintenance events, your power supply is probably not the culprit.
Run a stress test to push your power supply under load
A power supply can work fine during normal use but fail the moment you demand maximum power. Stress-testing software forces your CPU and graphics card to run at full capacity, which draws the most power your system can use. If the power supply fails during a stress test, it will fail during gaming or video editing too.
Download and run Prime95 (free, from mersenne.org) or MemTest86 (free, from memtest.org). Prime95 is easier to start with — just download it, extract the folder, and run "prime95.exe". Click "Just Stress Testing" when it asks, then let it run for at least 30 minutes. If your PC crashes, freezes, or shuts down during the test, stop immediately and note the time.
If Prime95 completes 30 minutes without crashing, run it for another hour. A power supply that's barely failing may hold up for 30 minutes but fail at 90 minutes. If your PC survives two hours of Prime95 without any shutdown or freeze, the power supply is almost certainly not the problem.
Listen for physical signs of a failing power supply
A power supply that's about to fail often makes noise before it stops working. Shut down your PC completely, wait 30 seconds, then turn it back on. Listen carefully during startup and the first minute of operation. A failing power supply may make a high-pitched whine, a buzzing sound, or a clicking noise.
Normal power supplies are nearly silent. If you hear any of these sounds, the power supply is likely failing internally. You should replace it soon, even if your PC hasn't crashed yet — a failing power supply can damage other components if it shorts out.
Also look at the back of the power supply (the part inside your case). If you see any burn marks, melted plastic, or a burnt smell coming from inside the case, the power supply has already failed and needs replacement immediately. Do not run the PC again until you've replaced it.
Check your power supply's age and wattage rating
Power supplies degrade over time. A power supply that's more than seven years old is more likely to fail, especially if it ran hot or was never cleaned. Look at the label on the back of your power supply (you may need to open the case to see it clearly). The label shows the wattage — usually 500W, 650W, 750W, or higher.
Compare that wattage to your system's power draw. If you have a high-end graphics card like an RTX 4080 or RTX 4090, a 500W power supply is undersized and will fail under load. Most modern gaming PCs need at least 750W. If your power supply is undersized for your components, it's working at maximum capacity all the time, which causes it to fail faster.
You can estimate your system's power draw by adding up the wattage of your CPU and graphics card, then adding 100W for everything else. If that total is within 100W of your power supply's rating, the supply is too small and should be replaced with a larger one.
Test your power supply's 12V rail with a multimeter
If you have a multimeter (a tool that measures electrical voltage), you can check whether your power supply is delivering the correct voltage to your components. This is more technical than the other tests, but it's still straightforward.
Shut down your PC and unplug it from the wall. Open the case. Locate the 24-pin power connector that plugs into your motherboard — it's the largest connector coming from the power supply. Set your multimeter to DC voltage mode. Touch the black probe to any black wire (ground) and the red probe to a yellow wire (12V rail). The multimeter should read between 11.4V and 12.6V. If it reads outside that range, the power supply is failing.
Repeat this test on a red wire (5V rail) — it should read between 4.75V and 5.25V. If both voltages are in range, your power supply is delivering power correctly. If either is out of range, the power supply needs replacement.
Know when to replace instead of test further
If your PC crashes randomly, shuts down under load, or won't start at all, and you've ruled out other causes (overheating, failing hard drive, bad RAM), the power supply is the most likely culprit. At that point, testing may confirm what you already suspect, but replacement is faster and cheaper than continuing to diagnose.
Power supplies are not repairable — if one fails, you replace it. A new power supply costs between $50 and $200 depending on wattage and quality. If you're not comfortable opening your case or running stress tests, you can take your PC to a repair shop and ask them to test the power supply. Most shops charge $30 to $60 for a diagnostic, which you can apply toward a replacement if the power supply is indeed the problem.
Frequently Asked Questions
Can a power supply fail partially and still work sometimes?
Yes. A power supply can deliver enough power for everyday tasks but fail when you game or run heavy software. This is why stress testing matters — it reveals failures that normal use won't trigger. If your PC crashes only during gaming or video editing, a failing power supply is a strong possibility.
How do I know if my power supply is the right wattage for my PC?
Add the maximum power draw of your CPU and graphics card, then add 100W for the rest of your system. Your power supply should be at least that total, ideally 100W to 200W higher for headroom. If you're unsure of your CPU or GPU's power draw, check the manufacturer's specifications online.
Is it safe to run Prime95 for hours on my PC?
Yes, Prime95 is designed for stress testing and is safe to run for as long as you want. However, your PC will get hot and use a lot of electricity. Make sure your case has good airflow and that you're not running it during peak heat hours. Stop the test immediately if your PC crashes or shuts down.
What's the difference between a power supply failing and a graphics card failing?
A failing graphics card usually causes visual glitches, artifacts on screen, or crashes only when you use graphics-heavy programs. A failing power supply causes random shutdowns, crashes under any load, or won't start the PC at all. Event Viewer logs will show kernel-power errors for power supply failures but not for graphics card failures.
Can I test the power supply without opening my case?
Yes. You can check Event Viewer, run Prime95, and listen for noise without opening the case. The only test that requires opening the case is the multimeter voltage check. If the other tests point to a power supply problem, you can replace it without doing the multimeter test.