Summary

• Cheaping out on PSU is unadvised
• Signs of PSU failure: smoke, no power, random restarts, or shutdowns, fan not spinning.
• Testing and replacing a faulty PSU isn't as hard as some would like you to think.

The power supply unit (PSU) is one of the most essential components of any PC build. The PSU, as the name suggests, is what powers up everything inside your PC. Without it, nothing would work, and you would be left with a very useless and large paperweight. While it is essential, it is also one of the components that gets looked over quite a bit, and people even try to cheap out on their PSU, which is never advised.

While all PSUs can become faulty over time, it is much more common in cheaper, unbranded, and unrated power supplies. When looking for a PSU, ensure it has an 80 PLUS or Cybenetics rating, as these will have been tested to meet certain standards for efficiency at different percentage levels of loads. If you are unsure but suspect your PSU is faulty, there are a few common problems that can help point you in the right direction as to where to look.

If you ever see or smell smoke or hear a pop/bang, unplug your PC from the outlet immediately and do not plug it back in until you are with someone who can test it properly.

What to look for

Knowing is half the battle

As with all faults on any product, there are usually some telltale signs to look for, and PCs are no different. Sometimes, there could be multiple reasons why a specific fault is happening, but knowing where to look and how to diagnose the issue properly can help you determine which component is faulty. You may need a bit of patience and some time, but there is no reason why you can't try to figure out where the fault lies should you experience issues with your PC. Some of the more common things to look for are:

1. No sign of life — If you have tried turning the PC on and nothing has happened, it could be the PSU. Check the motherboard, as when you turn the PC on, there should be some sort of light on it somewhere that illuminates it, even if it is for a short time. If you don't see any lights, the odds are that the PSU is faulty. If you do see lights, it could still be the PSU, but it could also be the motherboard or case power button, so you will need to dig a little deeper.
2. Smoke or burning smells — While not always related to the PSU, smoke can be a strong indication that something is wrong with the PC's power. If you saw smoke, did it come from the PSU? If you're not sure if you just smell some burning, disconnect the power immediately and see if you can find where it came from. Look at all the power connectors from the PSU to the motherboard and graphics card. If it is safe to do so, you can also smell the components to see if that can help you narrow down the cause of the burning smell.
3. Fan grinding or not working at all — Can you hear the PSU fan grinding, or is it not working at all? Many PSUs nowadays have a 0% RPM mode, which means the PSU fan won't turn on until the PC is under a certain load. There is also normally a switch to turn this on or off. However, all PSU fans should work when the PC is under a load, such as gaming. So, if your PSU fan isn't working, it may be faulty.
4. Getting shocked when touching the case — If you have to turn the PC on or touch it anywhere and feel a slight shock, something is wrong with the power to the system. There can be several causes, and, likely, something isn't grounded correctly. In this case, it's best to unplug the PC and look for any issue, such as broken USB ports, metal touching the motherboard, or something else that shouldn't be. If everything looks fine, it could be the PSU, so it's well worth checking it to be safe.
5. Powers off or crashes during POST/boot — There can be a couple different issues and outcomes here. Your PC could enter a boot loop if it doesn't pass the Power Good Measurement on first boot. Basically, it will look like the PC has crashed and is just trying to reboot itself. Or the PC could even turn off instantly or after some time. All of these can be indicators that the PSU is failing.
6. Power off under high loads — If you load a game or do any intensive task, your PC may completely lose power and turn itself off. This could be a sign that the PSU doesn't have enough juice to power up the components needed for the task at hand. In most cases, it will switch right off as if it has been unplugged from the outlet with no warning.
7. Random shutdowns, restarts, and blue screens - All of these can be telltale signs that there is something wrong with the PSU. Of course, they can also mean other components are failing as well, but never count the PSU out. If you are experiencing blue screens, it is well worth using a program like BlueScreenView to see what the actual issue is.

Testing the PSU to see if it really is failing

Always best to test just to be sure

There are several ways to test a PSU, some of which can even be done at home. Personally, I recommend taking it to a shop that has the proper tools, such as a load tester, to ensure it is tested properly. If you put a faulty PSU back into your PC, you could damage other parts, so it is better to be safe than sorry.

If you want to test at home, there are small PSU testers you can get from Amazon that will test the 3V, 5V, and 12V lines on the PSU. You simply plug all the PSU connectors into the tester as required, and it will jump-start the PSU, power it on, and give you the readings. This is a very basic test, but if there are any issues here, you know the PSU is faulty and should look into replacing it. Of course, even if the tester doesn't show any errors, it doesn't 100% mean the PSU isn't faulty, so keep that in mind.

Another option is to try a different PSU in the PC and see if it has the same issues. Of course, not everyone has a spare PSU just sitting around waiting for its chance to shine, but if you do, this is always a great way to check if your other PSU is faulty. If you plug the spare in and the issues go away, then it is highly likely the old PSU was the culprit and should no longer be used.

Replacing your faulty PSU

Make sure you pay attention to all the connectors

If your diagnosis shows that your old PSU is faulty and you're looking for a new one, you will want to pay attention to all the connectors to ensure the new PSU has what you need. Most power supplies will have a 24-pin motherboard connector, an 8-pin or 4+4 motherboard EPS connector (there may be two of these), at least one 8-pin that is typically a 6+2-pin connector for the GPU (there may be two of these or more), and some SATA and Molex connectors. Your PSU may even have the newer 12VHPWR connector for some of the latest NVIDIA graphics cards. You will want to take note of all the connectors plugged in on the old PSU and make sure the new PSU has the same connections. It is worth writing them down, as it can be confusing to remember them all after a while.

Once you have verified the new PSU has all the right connectors, you want to ensure that every connection plugged in with the old PSU gets plugged in again with the new PSU. This means making sure the power cables get plugged into the motherboard, graphics card, and anything else that requires power. I recommend leaving the PSU out of the system in its box when first trying it out. This way, if it should be faulty or something else seems to be the issue, it will be much easier to remove than if it was properly installed into the PC. While you won't want to leave the PSU out of your PC for too long, it will be fine for some initial testing.

If you have verified that the new PSU has all the cables/connectors you need and are comfortable that it isn't faulty, you can now install it into the PC. When replacing the PSU, make sure all the connectors are plugged in fully and that you haven't forgotten any connections you will need. Installing a new PSU is rather easy, especially if you've just taken the old one out, so you know all the connectors you require.

Should I really be doing this myself?

In this day and age, there really is no reason why you can't try some basic troubleshooting to see if your PSU is faulty. As mentioned, changing a PSU can be quite easy if you know what connections you need. Changing a PSU isn't a lengthy process and should not take more than an hour or two, even for a novice.

Just make sure that when unplugging any PSU connection from the PC, the PSU itself is unplugged from the outlet and has no power going to it. Also, never open up the PSU, as even when it is unplugged, it can still hold electricity and may shock you if not handled properly. Keep those two things in mind, and you should have your PC up and running again in no time.