The fastest way to check your power supply

Open your computer case and look at the power supply unit itself — it is a metal box, usually in the bottom rear corner. The wattage and model number are printed on a label on the side facing into the case. Write down the number that says "W" or "Watts" (it will be something like 500W, 650W, or 750W). This is the most reliable method because you are reading the actual hardware.

If you cannot or do not want to open the case, you can find the same information through your operating system, though the result is less certain. Both Windows and Mac have built-in tools that estimate your power supply wattage based on what components are installed, but they often guess low — the number they show may not match what is actually in your case.

Key Takeaways

  • The wattage label on the power supply itself is the only certain answer — look for the metal box in the bottom rear of your case and read the number marked "W".
  • Windows Task Manager and Mac System Information can estimate wattage, but they frequently underestimate and should not be your only source.
  • If you know your power supply model number, you can search the manufacturer's website to confirm the exact wattage.
  • The power supply wattage matters when you upgrade components like graphics cards or processors, because they draw power from the same unit.

Finding the label inside your case

Shut down your computer completely and unplug it from the wall. Wait a few seconds, then open the case — most modern cases have a side panel held by two or three thumbscrews or a latch. Once the panel is off, look toward the bottom rear corner. You will see a large metal box with a fan on one end. That is your power supply.

On the side of that box facing into the case, there is a white or yellow label with specifications printed on it. Look for a line that says "Max Output" or just lists a number followed by "W". That number is your wattage. You may also see "12V", "5V", and "3.3V" listed with their own wattage amounts — ignore those. The single large number is what you need.

Write down the model number too, which is usually near the top of the label. If you ever need to replace the power supply or check compatibility with new parts, having the model number lets you look up the exact specifications on the manufacturer's website (common brands are Corsair, EVGA, Seasonic, and Thermaltake).

Checking power supply info in Windows

Windows does not have a built-in tool that directly shows your power supply wattage, but you can see an estimate through Task Manager. Right-click the taskbar at the bottom of your screen and select "Task Manager". Click the "Performance" tab, then click "GPU" in the left sidebar. At the top right, you will see a line that says "Dedicated GPU Memory" — but more importantly, scroll down and look for any mention of power or wattage.

A more useful approach is to check what Windows thinks your system requires. Open Settings, go to "System" then "About", and scroll down to "Device specifications". This shows your processor and RAM, but not the power supply directly. However, you can take that information to a power calculator website (like OuterVision or be quiet!) and enter your components — it will estimate the wattage you need, which gives you a clue about what you likely have.

The most honest answer: Windows does not reliably report power supply wattage. If you see a number, it is an estimate based on your components, not a reading of the actual hardware. For a certain answer, you need to look at the label inside the case.

Checking power supply info on Mac

Click the Apple menu in the top left corner and select "About This Mac". Click the "System Report" button. In the window that opens, click "Power" in the left sidebar. You will see information about your battery (if you have a laptop) and power adapter, but not the internal power supply wattage in the way a desktop computer user needs.

For Mac desktop computers (iMac, Mac mini, Mac Studio), the power supply is not user-replaceable and the wattage is not shown in System Report. Instead, look up your exact Mac model on Apple's support website — search for "[Your Mac model] technical specifications" and the power supply wattage will be listed there. If you have a Mac laptop, the wattage of your power adapter is printed on the adapter itself, near where the cable connects.

What the wattage number means

The wattage is the maximum amount of electrical power your power supply can deliver to your computer at one time. A 500W power supply can deliver up to 500 watts. A 750W supply can deliver up to 750 watts. The higher the number, the more power-hungry components you can run simultaneously.

This matters because different components draw different amounts of power. A graphics card might draw 200W, a processor might draw 100W, and the rest of your system (motherboard, storage, fans) might draw another 100W. If your total draw exceeds what your power supply can deliver, the computer shuts down or fails to start. When you upgrade to a more powerful graphics card or processor, you may need a larger power supply to handle the extra load.

Power supplies are also rated by efficiency — you may see "80 Plus Bronze", "80 Plus Gold", or "80 Plus Platinum" on the label. This describes how much of the electrical power drawn from the wall actually reaches your components versus being wasted as heat. A higher rating means less wasted energy, but for the purpose of checking what you have, the wattage number is what matters most.

Using the model number to verify

Once you have the model number from the label, you can search for it on the manufacturer's website to confirm every detail. For example, if your label says "Corsair RM750x", go to Corsair's website, search for that model, and you will find the exact specifications including wattage, efficiency rating, and what cables come with it.

This is especially useful if the label is faded or hard to read. The model number is usually more legible than the wattage number, and it gives you a definitive source. It also helps if you are shopping for a replacement — you can look up whether your current model is still available or what the newer equivalent is.

Why you might need to know this

The most common reason to check your power supply wattage is before upgrading your graphics card or processor. Manufacturers list the recommended power supply wattage for each component, and if your current supply is too small, the new part will not work reliably. Knowing your wattage lets you decide whether you need to upgrade the power supply at the same time.

You might also need this information if your computer is shutting down unexpectedly under load, or if you are troubleshooting why a new component will not power on. A failing power supply sometimes shows symptoms like random restarts or the computer refusing to start, and knowing the wattage helps you determine whether a replacement is the right fix.

Frequently Asked Questions

Can I tell my power supply wattage just by looking at the case from outside?

No. The wattage is printed on a label inside the case, not on the outside. You have to open the case to read it. The only exception is if your power supply has a window or the label is visible through a vent, which is rare.

Is the wattage I see in Windows the same as what is on my power supply label?

Not necessarily. Windows estimates based on your components, and it often guesses lower than the actual wattage of your power supply. The label inside the case is the true number. Use Windows as a rough check, but verify by looking at the hardware itself.

What if I cannot open my case because it is locked or I do not have the key?

Contact the manufacturer or seller of your computer — they can tell you the power supply wattage based on your model number. If you built the computer yourself, check your purchase receipts or the documentation that came with the case. As a last resort, you can estimate based on your components using an online power calculator, though this is less reliable than the actual label.

Does a higher wattage power supply use more electricity if I do not need it?

No. A power supply only delivers the wattage your components actually draw. A 750W supply running a system that uses 300W will only draw about 300W from the wall (plus a small amount lost to heat). You do not pay extra for having more capacity than you use.

What should I do if the label is completely faded and unreadable?

If you can read the model number, search for it online. If even the model number is gone, you can estimate based on your processor and graphics card using an online power calculator, or you can contact a local computer repair shop — they can often identify the power supply by sight or by testing it.