The most reliable way to see what power supply you have is to look at the label on the unit itself. Every power supply has a sticker on one side listing its manufacturer, model number, wattage, and electrical ratings. If you can’t open your case or the label is hard to reach, there are a few other methods that work depending on your setup.
Check the Label on the Unit
Unlike your CPU or graphics card, your power supply doesn’t report its specs to your operating system. No software tool, including system monitors or hardware-detection utilities, can tell you what power supply you have. The information lives on a physical label stuck to the side of the unit.
To find it, shut down your computer and unplug the power cable from the wall. If you have a standard desktop tower, remove the side panel (usually held on by thumbscrews on the back). The power supply sits at the top or bottom rear of the case, depending on the design. You’re looking for a rectangular sticker that lists the brand, model number, total wattage, and a breakdown of power on each voltage rail (typically +12V, +5V, and +3.3V). The total wattage is usually printed in large text, something like “650W” or “850W.”
In some cases, the label faces the inside wall of the case or is positioned on the bottom of the unit, making it hard to read without removing the power supply entirely. If you can slide it out a few inches by removing its four mounting screws on the back panel, that’s usually enough to see the label without fully disconnecting all the cables.
Identify Your Power Supply Type by Looking at It
Once you have the case open, you can learn a lot just from the physical characteristics. Standard ATX power supplies, the kind found in most mid-tower and full-tower desktops, measure 150 mm wide by 86 mm tall. Their depth varies: budget units are often 140 mm deep, while higher-wattage models stretch to 160 mm or 180 mm. If your unit is noticeably smaller, around 125 mm wide and 63.5 mm tall, you likely have an SFX or SFX-L power supply, which is common in compact small-form-factor builds.
You can also tell whether your power supply is modular, semi-modular, or non-modular. A non-modular unit has every cable permanently attached in a thick bundle coming out of one side. A fully modular unit has a row of ports on its interior face where each cable plugs in separately, so you only connect the ones you need. Semi-modular units split the difference: the essential cables (the 24-pin motherboard connector, CPU power, and sometimes one graphics card cable) are hardwired in, while additional cables plug into open ports. Knowing this helps when you’re searching for replacement cables or planning an upgrade.
Look Up Specs for Pre-Built Computers
If you bought a pre-built system from Dell, HP, Lenovo, or a similar manufacturer, you may be able to skip opening the case entirely. These companies maintain online parts databases that let you search by your computer’s serial number or service tag, which is printed on a sticker on the outside of the case. On Lenovo’s support site, for example, you can enter your machine’s serial number or product type to pull up the exact power adapter or internal power supply spec. Dell and HP offer similar lookup tools through their support pages.
Keep in mind that many pre-built systems, especially slim desktops and all-in-ones, use proprietary power supplies with non-standard shapes and connectors. The wattage on these units tends to be lower than what you’d find in a custom-built PC, often in the 180W to 500W range. If you’re considering adding a dedicated graphics card to a pre-built machine, confirming the exact wattage and connector types is essential before buying anything.
Check Your Purchase History or Original Box
If you built your PC yourself, your power supply model is likely in an old order confirmation email from wherever you bought it. Searching your email for terms like “PSU,” “power supply,” or the names of common manufacturers (Corsair, EVGA, Seasonic, Thermaltake, be quiet!) can surface the receipt quickly. The original box, if you still have it, will list the full model number and wattage on the outside.
Why Your Power Supply Specs Matter
Most people search for their power supply details because they’re planning a hardware upgrade, usually a new graphics card. Modern high-end GPUs have significant power demands. The RTX 4090, for instance, draws around 450W on its own. Nvidia recommends at least an 850W power supply for that card, but several board partners push that recommendation to 1,000W or even 1,200W to give headroom for the rest of the system. A 450W GPU paired with a high-end processor and other components can easily pull 750W or more under load, which is why a bigger power supply provides a safety margin.
Beyond raw wattage, you should also check what connectors your power supply offers. Newer graphics cards from the RTX 40 series onward use a 16-pin connector called the 12VHPWR, which can deliver up to 600W through a single cable. Power supplies built to the ATX 3.0 standard include this connector natively. You can identify it by the “H+” symbol printed on the connector itself. Older power supplies require an adapter that converts two or three standard 8-pin connectors into one 16-pin plug. The adapter works, but a native connection is cleaner and generally considered more reliable.
If your power supply’s wattage is close to the minimum recommendation for the new component you want to install, that’s a sign it’s time to upgrade the power supply too. Running a unit near its maximum rated capacity consistently generates more heat, increases fan noise, and can shorten its lifespan. A comfortable target is a power supply rated for at least 20 to 30 percent more than your system’s expected peak draw.
What the Label Numbers Mean
The label on your power supply lists more than just total wattage. You’ll see separate lines for each voltage rail. The +12V rail is the one that matters most for modern PCs, because it powers your CPU and graphics card. If the +12V rail is rated for 500W on a 600W power supply, that tells you the actual power available for your most demanding components is 500W, not 600W.
You’ll also find an efficiency certification, usually listed as “80 Plus” followed by a tier: White, Bronze, Silver, Gold, Platinum, or Titanium. This tells you how much of the electricity drawn from the wall actually reaches your components versus being lost as heat. An 80 Plus Gold unit, one of the most common ratings in mid-range to high-end builds, converts at least 87% of input power at typical loads. Higher efficiency means less wasted energy and less heat inside your case, but it doesn’t affect the total wattage available to your hardware.