PSU wattage your PC needs for its CPU and graphics card.
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Add CPU, graphics card and the rest of the system, then 40% headroom. With a 125 W CPU, a 220 W graphics card and 75 W for the rest, the load is 420 W and 588 W with headroom: a 650 W PSU, running at 65% in the worst case.
Adds peak CPU and graphics power plus the rest of the system, then headroom for spikes and ageing. Rounds up to common PSU sizes; it does not replace the recommendation of the graphics card maker.
W = (CPU + GPU + rest) × (1 + headroom/100) → next common PSU sizeAdds peak CPU and graphics power plus the rest of the system, then headroom for spikes and ageing. Rounds up to common PSU sizes; it does not replace the recommendation of the graphics card maker.
All amounts use the same currency of your choice. These are estimates, not measurements or offers.
Choose the PSU wattage before you buy one or upgrade your graphics card. Use the peak power of each part, not the base TDP: PL2 for Intel processors and PPT for AMD; for graphics cards, the board power (TBP or TGP) on the maker spec sheet. For the rest of the system, 50 to 100 W usually covers motherboard, RAM, drives, fans and USB.
Power supplies are most efficient and quiet between 40% and 70% load, and headroom absorbs the brief spikes of modern graphics cards. If your graphics card maker recommends a larger PSU, use their figure. Choose quality over watts: a good 650 W 80 PLUS Gold unit is a better pick than an uncertified 850 W one.
Between 30% and 40% is typical. Use more if you plan to upgrade the graphics card or if yours is high end, with stronger power spikes.
The PSU turns at least 87-90% of the power it draws from the wall into usable power at typical loads. It describes efficiency, not wattage.
Many recent NVIDIA graphics cards use the 12V-2x6 connector. ATX 3.1 units include it natively and avoid adapters.