The rating on a computer power supply just tells you the maximum output, and the input that would accompany that amount of output. Power supplies are generally rated somewhat conservatively, so that even if you're using all of the peripherals at once, the actual power consumption will be lower than the power supply rating.
This is different from a TV or a refrigerator or other complete appliance, where the nameplate tells you the maximum expected consumption of that appliance as a whole. Custom-built computers (that gamers normally use) generally don't have a nameplate giving actual power consumption.
Dave