If you bought a pre-built computer (like an HP Pavilion or Dell XPS) and haven't modified it, you don't need to open the case.
Remove the side panel of your PC case (usually held by two thumb screws at the back).
This is the only way to be 100% certain of your PSU's brand, model, and total wattage. your PC and unplug it from the wall.
The PSU converts AC power from your wall outlet to DC power for your components. It functions independently of the operating system. While high-end motherboards can monitor voltages (12V, 5V, 3.3V) for safety, they generally cannot read the manufacturer sticker data from the PSU.
Look for a large . It will list the Brand (e.g., Corsair, EVGA), Model (e.g., RM750x), and Total Wattage (e.g., 750W).