You remember the graphics card you installed last year. The one the forums said needed “at least 500W.” You’d read that. You’d nodded. Then you’d told yourself it would probably be fine, because people online exaggerate, right?

You contort your phone beneath the PSU and snap a photo. Blurry, but readable. A sticker with logos, certifications, warnings in six languages, and then—smaller than the barcode, smaller than the serial number—the number you need: .

You don’t ask how to tell power supply wattage because you’re curious. You ask because something has gone wrong.

You order a new PSU that night. 650W, gold-rated, with a label you can read without dislocating your wrist. When it arrives, you install it slowly, carefully, and for the first time you notice how the cables feel different—thicker, firmer, less like cheap speaker wire and more like tools. You press the power button. The fans spin. The motherboard chimes. The machine breathes like it just woke from a long fever.

But the lights in your room stayed on. The monitor’s standby light blinked patiently. That’s when you started to suspect: the heart of the machine was failing.

You learn that wattage isn’t just a number. It’s a promise. And not all promises are kept. A $20 700W PSU is a fire in a box. A $100 450W unit from a trusted brand can run a system that draws 440W, because it’s built to deliver its rated power continuously, not just for the first five minutes. The sticker tells you peak wattage or sustained? Most don’t say. You have to know.

You start digging. Not into your PC, but into the arithmetic of your own mistakes. The CPU: 95W under load. The GPU: 220W peak. Motherboard, RAM, drives, fans, USB devices—add another 80W. Total: 395W. That leaves 55W of headroom, which sounds like a cushion but isn’t. Because power supplies lie. Not intentionally, but physically. A cheap 450W unit might only deliver 380W cleanly, and only at room temperature, and only when the stars align. On a warm evening, with dust in the fan, after two hours of gaming, your PSU was choking. The voltage dropped. The GPU panicked. The system pulled the emergency brake.