A modular power supply unit, inside a PC tower case.
Hannah Stryker / How-To Geek
Testing your computer's power supply unit is fairly simple. You can test the PSU with a basic jumper test, multimeter, or power supply tester. This will help you rule out power delivery issues as the source of your problem.

Experiencing computer problems? They could be caused by a failing (or outright fried) power supply unit. Here are some signs your PC’s PSU hardware is the problem—and three ways to test the PSU to see if it’s still working properly.

Signs Your PSU Is Failing

Before we talk about testing your computer’s power supply unit (PSU), let’s talk about common signs your PSU is failing. These are worth investigating and potentially replacing your PSU to avoid bigger problems like hardware failure or data loss.

The power supply unit is often overlooked in the PC troubleshooting process. But if you have unstable power, you’ll have numerous small and difficult-to-diagnose problems cropping up all over the place.

When a PSU fails, the best-case scenario is your computer won’t start, and you simply replace the bad PSU. In the worst-case scenario, it fails catastrophically and takes other hardware components with it. If there are any signs your PSU is failing, you should test it.

  • Smoke or burning smells can indicate component failure and electrical arcing, even before a complete PSU failure.
  • Your computer shocks you. The shielding and grounding in your computer have failed somewhere.
  • Your computer randomly shuts down or blue screens. If you can’t pinpoint it to a software problem or a new piece of hardware like a GPU, it’s possible issues with your PSU are causing voltage drops and shutdowns.
  • Boot stability is inconsistent. If your computer errors out or crashes intermittently on boot, there’s a good chance your PSU is on its way out.
  • Noise from the PSU. Whether it’s fan grinding (the fan in most PSU models is not user-serviceable) or high-pitched whining or buzzing from the PSU, any noise beyond the slight hum of the fan is usually a bad sign.

If you’re troubleshooting a ghost-in-the-machine type problem that seems unsolvable no matter how many times you reseat hardware components, reinstall drivers (or even the whole OS), or otherwise deep dive into fixing your PC, you absolutely should test your PSU.

We’d go even further and suggest that you not only test a PSU if you suspect power supply issues are behind your current PC woes, but you should also test a brand new PSU before installing it in your computer.

The chances of getting a defective PSU from a reputable manufacturer are slim, but testing a PSU is so easy there’s no reason not to take a moment to do so before mating that PSU with hundreds of dollars worth of hardware.

How to Test Your PSU

There are three ways to test your PSU. One requires little more than a paperclip or a scrap of wire. The others require inexpensive tools that, while you might not have them on hand, are easy to acquire.

Warning: Do not open your power supply unit at any point during the diagnostic process. The internal components of a power supply unit are not user serviceable. Handling them without proper equipment and training can give you a lethal shock.

Testing Your PSU with a Basic Jumper Test

Testing a PSU with a piece of wire.
Jason Fitzpatrick

The jumper test is the least detailed test. In a pinch, however, it will at least tell you if your PSU can power on (or if it’s damaged in such a way that it can’t even spin up and provide power to your computer).

To perform a jumper test, you simply need a paper clip or a piece of wire with a gauge of 16AWG or 18AWG. You can purchase a jumper bridge tool, but it’s a bit overkill for most people unless you troubleshoot power supply units all day.

With your wire or paper clip jumper handy, here’s how to test whether your PSU can turn on. These instructions assume that your PSU is currently inside your computer, and you’re starting the troubleshooting process from there.

Color-cored ATX power pinout diagram.

Refer to the ATX power pinout diagram above while following the instructions. Even if your PSU uses non-standard colors for the cables (such as all black, or a rainbow gradient), the pinout pattern should still be standard with the “Power On” pin located four slots over from the front side of the connector.

  1. Unplug your computer’s PSU from the wall.
  2. Open your computer’s case to access the PSU.
  3. Unplug the large 24-pin connector from the motherboard.
  4. Use your jumper to bridge the green wire (pin 16) to an adjacent black wire (pin 15 or 17).
  5. Plug the PSU back in.

Bridging the green “Power On” wire to any black ground wire on the motherboard connector and then plugging your PSU back in should cause the fan on your PSU to spin along with any power indicator lights (if present) to illuminate.

If bridging the green wire to an adjacent black wire does not turn on your PSU, it is safe to assume that the PSU is damaged and inoperable. If the unit is brand new, you should return it. If it’s within warranty, you should file a claim.

Testing Your PSU With a Multimeter

Testing a PSU with a multimeter.
Jason Fitzpatrick

If you have a multimeter in your toolbox, you can use it to perform a more detailed test on your power supply unit.

While the jumper bridge test will only tell you if the power supply unit turns on, you can use a multimeter to test the connectivity and voltage between all the different pins. To do so, you simply need to short out the Power On pin and an adjacent ground pin with a jumper, as we did in the previous section.

INNOVA 3320 Auto-Ranging Digital Multimeter

A good multimeter is useful for so many projects around the house.

Then you can connect one of your multimeter’s probes to one of the ground pins, and then to each of the other pins on the connector pinout one by one to check if the voltage is correct.

Our guide to testing your PSU with a multimeter includes detailed instructions for testing, not just the 24-pin motherboard connector but also your GPU and other power connectors.

Testing Your PSU With a PSU Tester

A PSU tester.
Jason Fitzpatrick / How-To Geek

Using a multimeter to test your PSU is great because many people have multimeters on hand (or can borrow one from a friend or neighbor). But it does involve a lot of fussing with the multimeter, poking pins, and it’s hard to test small connectors like fan headers and SATA connectors.

Fuhengli ATX Power Supply Unit Tester

This simple all-in-one unit tests ATX power 20 and 24-pin connectors as well as PCI-e, MOLEX, and SATA power connectors, too.

Fortunately, dedicated PSU testers are quite inexpensive. Further, testing your PSU with a PSU tester is unbelievably simple. You just plug in the cables you want to test, turn on the PSU, and read the LCD screen readout on the tester.

Power Supply Unit Frequently Asked Questions

If reading this article in a bid to troubleshoot possible PSU problems has you giving serious thought to your PSU for the first time, we’re here to help! Here are some common questions people have about power supply units.

Can You Have Too Big of a PSU?

You can hurt your wallet by buying a super-size premium PSU when you don’t actually need it for your particular build, but it won’t hurt your computer.

You can’t buy too big of a PSU. Your computer will simply use as much power as it needs and leave the rest of the potential capacity of your PSU untapped.

Do Oversized PSUs Waste Power?

Putting a powerful high-watt PSU in your computer will only use as much power as your hardware requires. So in that regard, there won’t be wasted energy by way of excessive consumption. However, there is one way that an oversized power supply unit can cost you money.

Power supply units convert the alternating current (AC) supplied by the wall outlet in your home into the direct current (DC) used by your computer. The process is most efficient when the power requirements of your PC are around 50% of the rated capacity of the PSU.

If your PSU’s wattage rating is very close to the actual demands of your PC (such that it’s running at nearly 100%) or extremely high compared to your PC’s needs (such that it’s running very low at 10-20% of the total capacity), there will be a decrease in efficiency. Practically speaking, however, power supply inefficiencies will only cost you a dollar or two a year, so that’s hardly a reason to avoid buying a higher-rated PSU.

What Do “80 Plus” Power Certifications Mean?

When shopping for a power supply unit you’ll quickly come across PSU power certification ratings like “80 Plus Gold” and “80 Titanium.”

These ratings are an industry standard that indicate how efficient a power supply unit is under an 80% power load. The most basic “80 Plus” certification indicates that the PSU is 80% efficient when placed under a 50% load. The efficiency increases with each tier up to “80 Plus Titanium,” which offers 94% efficiency under a 50% load.

Does PSU Quality Really Matter That Much?

The poor PSU might get almost zero press time and none of the glory that flashier components like GPUs and advanced multi-core CPUs get, but the humble PSU is the bedrock of a stable PC build.

You don’t need to buy the most premium PSU on the market, but you want to avoid no-name white-label PSUs. Stick to established companies with solid track records like EVGA and Corsair. Your PSU shouldn’t be the PC component you splurge on the most, but it shouldn’t be an afterthought.

Can I Reuse My PSU in a New Computer?

You can absolutely reuse an older PSU in a new computer. Unlike many computer components that end up incompatible with newer builds (such as outdated RAM), PSUs are standardized, sturdy, and one of the PC components you should consider reusing.

While we don’t recommend reusing a twenty-year-old PSU from your old college computer in a new build, you can easily get ten years out of a high-quality PSU, so there’s no reason to buy a new one every time you rebuild your gaming PC unless your new build has much higher power requirements.

Can I Reuse My Old PSU’s Cables?

If you buy a new PSU to replace your old one, and they both have modular cables, you might be tempted just to unhook the cables from the old unit and plug them into the new one.

We advise against reusing modular PSU cables because it can have catastrophic consequences. The physical power connections and their pinouts are standardized on the end of the cables (the part you plug into your motherboard or GPU), but the connections on the PSU side are not, and the “pinout” of the PSU is manufacturer dependent.

This means if you plug a modular cable from one manufacturer into the PSU of another manufacturer, you have no guarantee the right voltages are going to the right pins resulting in a situation not unlike plugging in an extension cord without realizing the hot, neutral, and ground wires have been switched around.

If you wish to reuse them, be sure to identify and test your modular PSU cables to ensure the device side pinouts are correct.

If You Upgrade Your GPU, Do You Need a New PSU?

You don’t necessarily need to upgrade your PSU if you upgrade your GPU. If your new GPU has power demands that will push your computer’s total power consumption beyond the load rating of your current PSU, you will need to upgrade.

Before you upgrade, however, it’s wise to calculate your PC’s power load with the new GPU instead of assuming you need to upgrade the PSU along with the GPU.

Can You Upgrade an Existing PSU?

You can upgrade an existing PSU, but with a noteworthy caveat. If you built your own PC, ordered it from a custom PC builder, or it is a prebuilt computer that uses standard ATX connectors, then it should be trivial to upgrade your power supply unit.

Several manufacturers, notably Dell and HP, have used non-standard power connectors over the years, making it a hassle to upgrade their prebuilt computers. If you attempt to swap out their propriety PSUs with a standard off-the-shelf PSU, you’ll find that the connectors aren’t compatible, the wiring pinouts don’t match, or both.

While it’s possible to work around that with third-party adapters or even redo the wiring pinouts yourself, it’s probably not worth the hassle, and it’s better to replace the PSU with an identical OEM model or upgrade the entire machine.

Are the PSUs in Prebuilt Computers Low Quality?

The power supply units in prebuilt computers are not inherently low-quality. Some prebuilt computers are made by shops that use off-the-shelf parts, and you’ll find a quality EVGA power supply in your “prebuilt” machine just as if you’d picked the part yourself and installed it.

But many prebuilt computers, especially the mass-produced low and mid-level offerings you at your local big-box electronics stores, have terrible no-name PSUs produced by the lowest bidder. This is one of the many reasons we recommend using a checklist when buying a prebuilt computer to ensure you get the build quality you want.

Can I Use Two PSUs in a Computer?

It might seem like a strange question if the thought hadn’t crossed your mind, but it makes sense. When you need more RAM or storage in a computer, you typically add more, so why not do the same with a PSU? If you need 400 more watts because of your new GPU, why not just stack another PSU on the pile?

Using two PSUs with one regular desktop computer is possible, but it’s not a very elegant, efficient, or safe solution. Unless you have a specific use case, we recommend upgrading your power supply unit and enjoying a simple all-on-one experience without any questionable hacks or workarounds.

Is Capacitor Aging Really a Concern in PSU Longevity?

When you get into the weeds of PSU comparisons and performance, you’ll find articles and discussions about capacitor aging in power supply units.

When buying a PSU from a reputable manufacturer with a good warranty, this isn’t really something most people need to worry about. If you really want to max out the life of your PSU, however, you can look for manufacturers that use high-quality solid capacitors (instead of less expensive liquid ones) and offer 10-year warranties—an excellent indication they expect their product to last.

Profile Photo for Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Senior Smart Home Editor at How-To Geek. He has over a decade of experience in publishing and has authored thousands of articles at How-To Geek, Review Geek, LifeSavvy, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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