What PSU do I need for a Radeon RX 7900 XTX?

Why the answer is a range

A Radeon RX 7900 XTX is rated at 355 W of board power, and AMD recommends a 800 W supply for it. That single figure has to cover every processor anyone might pair with the card, which is why the honest answer depends on yours: across the 26 processors here this card needs anywhere from 800 W to 850 W.

With a Ryzen 7 7800X3D the whole system draws 561 W at once — 355 W for the card, 162 W for the processor at its power ceiling, and 44 W for the board, memory, drives and fans. That calls for 800 W, leaving the supply at 70% of its rating rather than sitting on top of it.

The 50 W spread across processors is not a rounding difference. A Ryzen 5 at 88 W and a Core i9 at 253 W are 165 W apart before anything else is counted, which is more than a whole supply size. Picking from the table below rather than from the card's blanket recommendation is the difference between buying the right unit and buying two sizes too big.

On 6 of those pairings the arithmetic asks for more than AMD's 800 W, because the processor is heavier than a blanket recommendation can assume. On 16 it asks for less, and the recommendation here stays at the vendor's number anyway — they know how their own board behaves when it spikes, and this calculator deliberately does not model that.