Wattage Headroom
The gap between a power supply's rated capacity and the actual sustained draw of the system, kept large enough for cool, efficient, reliable operation.
Wattage headroom is the difference between a power supply's rated output and the actual sustained power your rig pulls under load. Leaving generous headroom lets the PSU run in its most efficient band, typically around 40 to 70 percent of its rating, where it stays cooler, quieter, and lasts longer. For a single mid-range GPU build drawing 250 to 400 watts sustained, a 650 to 750 watt unit provides comfortable headroom. Too little headroom forces the PSU to run hot near its limit, while excessive headroom wastes money on capacity you never use. Sizing for sensible headroom, rather than chasing the biggest number, is the mark of a well-planned mining build.