How many watts do I need for a high-end GPU like an RTX 4080 or 4090?

Across the reviewers we read, the prevailing guidance is 850W for an RTX 4080-class build and 1000W for an RTX 4090 or RTX 5090, especially when paired with a power-hungry CPU like a Core i9 or Ryzen 9. A few r/buildapcsales commenters note their 1000W units have powered RTX 5090 systems without issues, but headroom matters because ATX 3.1 PSUs need to absorb transient spikes.