A PSU converts wall AC into DC for PC components. Start with the GPU maker’s recommendation, then account for the CPU, drives, fans and peak loads. An 850 W rating describes output capacity. 80 PLUS grades such as Gold measure efficiency under test conditions. Check protections, voltage stability, noise and warranty separately.
ATX 3.x addresses short power spikes. Check the GPU’s required connector and count, including 12V-2x6 where applicable. Check case depth and cable clearance. Use the supplied modular cables or ones approved for that exact PSU. Seat GPU power connectors fully and avoid sharp bends near the plug.