Generally speaking, the optimal power draw for most PSUs is around the 50% mark, maybe going as high as 70%. Personally, I wouldn't want to run a PSU anywhere close to 90% load on a regular basis. Theoretically it should be 'safe' to do so, but I've had plenty of bad experiences in the past with PSUs failing at 80% or higher loads if they're subjected to those on a regular basis.
Anyway, based on what has been said by Nvidia, I fully expect power use to be higher this round than in previous releases. It's possibly just to give ray tracing hardware enough headroom to run at higher performance, it's possibly because AMD is closer than last launch. We'll hopefully get the official word tomorrow, but if an RTX 3090 has a rated board power (minus USB-C) of 350W, you can expect Nvidia's recommended PSU for such a card to be 850W -- add 100W for CPU, then another 100W for other devices, and then provide a 50% buffer.