PSU wattage
The maximum continuous power output a desktop power supply unit can deliver, in watts. A correctly sized PSU runs efficiently and quietly; an undersized one shuts down under load.
PSU sizing combines CPU TDP, GPU peak draw, and headroom for transients. Modern high-end GPUs (RTX 4090, RX 7900 XTX) draw 600+ W in millisecond spikes — far above their average pull — so the PSU's transient response matters as much as the watt label.
Sizing rule of thumb
Add CPU TDP + GPU peak board power, then add 30–40% headroom. A 250 W CPU plus 450 W GPU points to an 850–1000 W PSU.
Efficiency ratings
80 Plus Bronze / Gold / Platinum / Titanium describe efficiency under load. Gold (90% at 50% load) is the modern baseline. Higher ratings cost more but save little electricity unless the PC runs at full tilt for many hours daily.
ATX 3.0 / 3.1
New PSUs ship with the 12V-2x6 connector for native NVIDIA 40/50-series support and better transient handling. Older 12VHPWR adapters are functional but more fragile.