This is likely a cautious recommendation on nVidia's part.
A 2080 Ti + 8700k system used 450W (nvidia recommended a 650w psu). While high end CPUs have gotten a bit more power hungry with higher core counts on the 10900k/10700k/3900x/3950x, I'd be shocked if a 650W PSU couldn't handle a mainstream CPU + 3080.
https://www.techspot.com/review/1701-geforce-rtx-2080/page4....
nVidia's recommendation is based on "we don't want people pissed off because they put it in a system with a 3990wx at the recommended PSU capacity and it didn't work"