How to Test the Power Supply Unit (PSU) in Your PC

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A step-by-step guide to testing your PC's power supply

Co-authored by Luigi Oppido and Darlene Antonelli, MA

Last Updated: December 11, 2024 Fact Checked

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Using a Paperclip

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Using a Power Supply Tester

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Using a Multimeter

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Expert Q&A

If your desktop PC won't turn on, is stuck in a reboot loop, periodically powers down, or gives you frequent blue screen errors, you might have a failing or dead power supply (PSU). Fortunately, it's easy to check your computer's power supply using a power supply tester, which you can get from any store that sells computer parts. If you can't find a PSU tester, you can check to see if the power supply is completely dead by doing a quick paperclip test or by measuring the power supply's voltage using a multimeter. This wikiHow article will teach you three easy ways to check the power supply in your PC desktop computer.

Quick Steps

Turn off your computer.
Open the case and remove plugs from the power supply unit.
Find the green and black pin (location varies by manufacturer).
Use a paperclip to connect the specified pins.
Plug the PSU into power and look at the fan to see if it spins.

Method 1

Method 1 of 3:

Using a Paperclip

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Shut down and unplug your computer. If you haven't already done so, you will need to turn off your computer and completely remove it from power. Use the switch on your desktop PC to flip the power switch to the Off position, and remove the AC power cord.^{[1]
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Luigi Oppido
Computer & Tech Specialist

Expert Interview. 13 November 2020.}
2
Open your computer case and unplug all cables from the power supply. Disconnect the power supply cables from all of the components inside the case once you've opened the case. Follow each cable from the power supply to the component to make sure that everything is completely unplugged.^{[2]
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Luigi Oppido
Computer & Tech Specialist

Expert Interview. 13 November 2020.}
- It might be helpful to take a photo of where everything is connected before you start disconnecting wires.
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3
Make a paper clip tester. You can use a paper clip to help test your power supply and trick it into thinking it has been switched on. To do this, straighten a paperclip and then bend it into a “U” shape.
- This paperclip will act as the pins that are inserted into the power supply that gives it the “Power ON” signal.
It is typically the largest connector for the power supply.
5
Find the green pin and black pin (make-specific). You will insert the paperclip's ends into the green pin (there should be only one) and a neighboring black pin. This is make-specific, so check the manual or online to find out which pins you should use for your specific power supply.
- For example, a Corsair PSU requires you to short pins 16 & 17 while an ATX power supply requires you to use pins 15 & 16.^{[3]
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- Before you do this, double-check to make sure that the power supply is completely disconnected from any power outlet, switched off, and not connected to any computer components. Failing to do so means sticking a metal paperclip into a live power supply with electricity running through it. You can shock yourself and cause physical harm as well as damage your computer.
Once you have placed the paper clip into each of the pins, place the cable somewhere where it won’t be disturbed.
As long as your paper clip stays in place, the power will run through the device.
8
Check the fan. Once the power supply is receiving power, you should be able to hear and/or see a fan moving. This will let you know that the power supply is at least working. If the power supply does not turn on at all, double-check your pins (after unplugging) and try again. If it still does not turn on, it is most likely dead.
- Many power supplies run the fan for only a second after it powers on; that is the zero-RAM feature. Don't be alarmed that the fan isn't continuously running! The fan briefly turning on means that your power supply is at least supplying output.
- This test will not tell you if the power supply is functioning as it should, just that it is turning on. You will need to perform the next test to ensure that it is outputting correctly.

Method 2

Method 2 of 3:

Using a Power Supply Tester

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1
Get a Power Supply Tester from any electronics store. Most stores that sell computer parts also sell PSU testers. You can also find them online easily at retailers like Newegg.com, MicroCenter, and TigerDirect.
- Unlike poking around with pins using a multimeter, a PSU tester is plug-and-play. All you'll need to do is disconnect the power supply from your computer, connect the PSU tester to the power supply and CPU, and power on your PC to check the power supply.
If you haven't already done so, you will need to turn off your computer and completely remove it from power. Use the switch on your desktop PC to flip the power switch to the Off position, and remove the AC power cord.
3
Open your computer case and disconnect all components from the power supply. Follow the cables leading from the power supply to other components, like the motherboard, and disconnect them. Leave the cables connected to the power supply, but disconnected from the other components.^{[4]
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Expert Source

Luigi Oppido
Computer & Tech Specialist

Expert Interview. 13 November 2020.}
- It might be helpful to take a photo of where everything is connected before disconnecting wires.
4
Connect the power supply's 24-pin power connector and 4-pin power connector to the PSU tester. Depending on your power supply, you might actually have a 6-pin or 8-pin secondary connector. If there are multiple, connect the 24-pin connector, and just one of the other connectors, to the matching locations on your PSU tester.
- The PSU tester should still be turned off at this point.
It's best to plug directly into the wall rather than a power strip or surge protector.
6
Turn on the PSU tester. Once the tester is on, you should hear the internal power supply fan start to run.
- Some PSU testers require you to hold down a button to check the power supply.
7
Check the voltage and PG value. It's normal for the voltages recorded not to match the suggested voltages exactly, as long as they are within a 5% range. If any values are outside of the suggested range, the tester will alert you with an LED or sound, depending on the tester. Any out-of-range values indicate it's time to replace your power supply unit.
- The PG value should be within 100-500 MS. If the PG value is way too high, your computer will constantly reboot or shut itself down. A new power supply should fix that problem.

Method 3

Method 3 of 3:

Using a Multimeter

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1
Turn on your multimeter and set it to VDC (Volts DC). If you don't have a power supply tester, you can use a multimeter to check the voltage of your power supply.
- If your multimeter does not have an auto-range feature, set it to 10.00V.
2
Connect your multimeter to your power supply. Connect the negative probe on the multimeter (it's black) to any ground-wired pin (find them by searching your PSU online), and connect the positive probe (it's red) to the first power line.
- You should repeat this test for every line that carries a voltage, like pins (for ATX PSUs only) 1, 2, 4, 9, 10, 11, 12, 13, 14, 20, 21, 22, and 23. For Corsair power supplies, test pins 1, 2, 4, 6, 9, 14, 21, and 23.
3
Read the multimeter output. If the voltages shown are within an acceptable range (you can find a list of acceptable ranges for your specific power supply online), it's ok to use. If there are any outside the range, you probably need to replace it.
- Even with your current readings, you aren't done! You need to test if your PSU performs under pressure.
4
Connect everything to power again and turn your computer on. In the next steps, you'll turn on your computer and use it normally without the case on the tower. Don't forget to plug in the power to your video card (if it requires one), your hard drive, and your optical drives.
- You can briefly use your computer without the case on, but just be careful not to ruin the insides of your computer!
- If the computer won't start without the case, you must remove the appropriate jumper on the motherboard. The manual for your computer should explain how you do this.
- Before you turn the power on, remove the paperclip you previously set up!
Connect the negative probe on the multimeter (it's black) to any ground-wired pin (find them by searching your PSU online), and connect the positive probe (it's red) to the first power line.
6
Read the multimeter output. If the voltages shown are within an acceptable range (you can find a list of acceptable ranges for your specific power supply online), it's ok to use. If there are any outside the range, you probably need to replace it.
- Repeat this test for every pin that has a voltage.
7
Re-attach the case to your computer tower. Since testing is complete, you can put the case back on your computer tower.
- If you are still having computer errors, or your computer will not start, move on to other troubleshooting steps. The first place to check will be your motherboard.

Expert Q&A

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Question

If I'm testing a power supply, which plug do I test?

Luigi Oppido
Computer & Tech Specialist
Luigi Oppido is the Owner and Operator of Pleasure Point Computers in Santa Cruz, California. Luigi has over 25 years of experience in general computer repair, data recovery, virus removal, and upgrades. He is also the host of the Computer Man Show! broadcasted on KSQD covering central California for over two years.

Luigi Oppido

Computer & Tech Specialist

Expert Answer

You should test all of them. So check the SATA plug, the molex plug, the A TX plug, the video power card, and whatever other plugs you have on your power supply. All of those plugs should be working if your power supply is functional.

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Question

Can a power supply still work if one of the pathways is bad?

Luigi Oppido
Computer & Tech Specialist
Luigi Oppido is the Owner and Operator of Pleasure Point Computers in Santa Cruz, California. Luigi has over 25 years of experience in general computer repair, data recovery, virus removal, and upgrades. He is also the host of the Computer Man Show! broadcasted on KSQD covering central California for over two years.

Luigi Oppido

Computer & Tech Specialist

Expert Answer

Yes, theoretically, a power supply should still be able to function if only one of the pathways is bad. It can depend on which pathway it is, but it's certainly possible.

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Question

How can you tell if a power supply is bad?

Luigi Oppido
Computer & Tech Specialist
Luigi Oppido is the Owner and Operator of Pleasure Point Computers in Santa Cruz, California. Luigi has over 25 years of experience in general computer repair, data recovery, virus removal, and upgrades. He is also the host of the Computer Man Show! broadcasted on KSQD covering central California for over two years.

Luigi Oppido

Computer & Tech Specialist

Expert Answer

The only way to know for sure is to use a power supply tester. You can make some solid guesses based on how your computer is behaving, but there's no way to know for sure without a power supply tester.

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Thank you for your feedback.
If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
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