Start with the label on the power supply itself

The fastest way to check your power supply is to look at the label stuck to the unit. If your computer is still under warranty or you are not comfortable opening the case, this is your only option — and it tells you almost everything you need to know.

Locate the power supply unit (PSU), which is usually a metal box in the bottom rear corner of a desktop tower. On one side of that box is a white or silver label listing the wattage, model number, voltage, and sometimes the manufacturer. Write down the wattage number — this is the maximum power the supply can deliver, measured in watts. A typical office computer uses a 300–500 watt supply; gaming or workstation builds often use 650–1000 watts or more.

If you cannot see the label clearly or your computer is a laptop, you will need to check the BIOS or use system information tools instead. For laptops, the wattage is usually printed on the power adapter brick itself.

Key Takeaways

  • The power supply label shows the wattage and model number without opening your case, and this information is usually all you need to know whether the supply is adequate.
  • You can also check wattage through your computer's BIOS menu by restarting and pressing Delete, F2, or F12 during startup, though not all BIOS versions display this information.
  • Windows and Mac both have built-in system information tools that show the power supply model and sometimes wattage without requiring you to open the case.
  • If your computer is shutting down unexpectedly under load, making noise, or failing to start, the power supply may be failing even if the label shows adequate wattage.
  • Replacing a power supply costs between $50 and $200 depending on wattage and quality, and is one of the most common and straightforward repairs a computer owner can make.

Check power supply information through Windows system tools

Windows does not always display power supply wattage in its built-in tools, but it will show you the model and manufacturer, which you can then look up online. Open the Start menu, type "System Information," and click the result. Look for entries labeled "System Manufacturer" and "System Model" — these often tell you which PSU came with your computer.

For more detailed hardware information, you can also use the Device Manager. Right-click the Start menu, select "Device Manager," and expand the "Batteries" section if present. This will not show the PSU directly, but it confirms whether Windows recognizes your power hardware. If you see warnings or errors here, the power supply or its connection may be failing.

A third option is to read CPU-Z or GPU-Z, free tools that display detailed hardware specifications including power draw estimates. These programs show how much power your system is currently using, which helps you determine whether your PSU has enough headroom. If your system is drawing 400 watts and your PSU is rated for only 450 watts, you are running too close to the limit.

Access the BIOS to view power supply details

Your computer's BIOS (Basic Input/Output System) sometimes displays power supply information during startup. Restart your computer and watch the screen carefully. As soon as you see the manufacturer logo, press Delete, F2, F10, or F12 repeatedly — the correct key depends on your computer's maker and will usually be shown on the startup screen. You are aiming to enter the BIOS setup menu before Windows loads.

Once in the BIOS, look for a section labeled "System Information," "Main," or "Power." Not all BIOS versions show PSU wattage, but many display the model number or power status. If you find the information, write it down. If the BIOS does not show power supply details, exit without saving (usually by pressing Escape) and try one of the other methods instead.

Entering the BIOS is safe as long as you do not change any settings. If you are unsure which key to press or feel uncomfortable navigating the menu, stick with the Windows tools or the physical label method instead.

Check Mac power supply information

Mac computers, especially laptops, have power adapters rather than user-replaceable power supplies. To find the wattage, look at the power brick itself — the large rectangular adapter that plugs into the wall. The wattage is printed on a label, usually on the bottom or side, and is measured in watts (W). A MacBook Air typically uses a 45–65 watt adapter, while a MacBook Pro uses 85–140 watts depending on the model.

For desktop Macs (iMac, Mac mini, Mac Studio), you can check the power specifications through the Apple menu. Click the Apple logo in the top left, select "About This Mac," then click "System Report." Look for "Power" or "Power Supply" in the Hardware section. If this information is not listed, the wattage is usually available on Apple's official specifications page for your specific model.

Signs that your power supply is failing

Even if the label shows adequate wattage, a power supply can fail and cause problems. Watch for these warning signs: your computer shuts down suddenly during heavy use (gaming, video editing, or large file transfers), the computer fails to start even though it was working the day before, you hear a loud humming or buzzing noise from inside the case, or the power cable feels hot to the touch.

If you see any of these symptoms, the power supply may be failing even if it still powers on. A failing PSU can damage other components like the motherboard or graphics card, so replacing it sooner rather than later is usually the safer choice. You do not need to wait for it to stop working completely.

Another sign is if your computer randomly restarts or freezes under load. This can also indicate a failing power supply that cannot deliver stable power to all components at once. If you have already ruled out overheating (by checking that fans are running and vents are clear), a power supply test or replacement is the next step.

How to physically inspect the power supply

If you are comfortable opening your computer case, you can visually inspect the power supply for damage. Power down the computer completely, unplug it from the wall, and wait at least 30 seconds. Then open the case according to your computer's manual — usually this means removing one or two side panels held by screws or latches.

Look at the power supply unit itself. Check for burn marks, discoloration, or visible damage to the casing. Look at the cables coming out of the PSU — they should be intact with no fraying, melting, or exposed wires. If you see any of these signs, the power supply needs replacement.

Do not attempt to open the power supply itself or touch the internal components. Power supplies store electrical charge even when unplugged, and touching the wrong part can cause serious injury. If you need to replace the PSU, a computer repair shop or a knowledgeable friend can help, or you can purchase a replacement unit and follow a manufacturer's installation guide.

Understanding power supply wattage and your needs

Power supply wattage is the maximum power the unit can deliver, but your computer does not use that much power all the time. A gaming computer might use 400 watts during intense gameplay but only 100 watts during web browsing. The PSU needs to be large enough to handle your peak demand without running at full capacity constantly.

As a general rule, your power supply should be rated for at least 20 to 30 percent more than your system's peak power draw. If your computer uses 400 watts at full load, a 500-watt PSU is adequate but tight; a 550 or 600-watt PSU gives you more headroom and longer lifespan. Undersized power supplies run hot, fail sooner, and can damage other components.

If you are upgrading your graphics card or adding new components, check whether your current PSU has enough wattage. Most graphics card manufacturers list the recommended PSU wattage on their product page. If your current supply falls short, you will need to replace it before installing the new component.

Frequently Asked Questions

Can I tell if my power supply is failing without opening the case?

Yes. If your computer shuts down unexpectedly during heavy use, fails to start, makes loud humming or buzzing sounds, or the power cable feels hot, the PSU is likely failing. You can also check the label for the wattage and compare it to your system's power draw using free tools like CPU-Z to see if the supply is undersized.

What if I cannot find the power supply label?

Use Windows System Information or the BIOS menu to find the power supply model number, then search for that model online to find the wattage. You can also take a photo of the inside of your case and post it to a computer forum where experienced users can identify the PSU by sight.

Is it safe to replace my own power supply?

Replacing a power supply is straightforward if you follow safety steps: power down completely, unplug from the wall, wait 30 seconds, and disconnect the cables from the PSU before removing it. Do not open the PSU itself. If you are unsure, a computer repair shop can do it for $50–$100 in labor plus the cost of the new unit.

How often do power supplies need to be replaced?

A quality power supply typically lasts 5 to 10 years depending on usage and heat exposure. If your computer is in a hot environment or runs continuously, the PSU may fail sooner. Budget for replacement every 5 to 7 years if your computer is heavily used.

Does a higher wattage power supply use more electricity?

No. A power supply only delivers the power your components actually draw. A 1000-watt PSU powering a system that uses 300 watts will draw only 300 watts from the wall, not 1000. A larger PSU straightforward gives you headroom and runs cooler, which can extend its lifespan.