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Only had a few hours with my 3090 but so far, so good with my Corsair 650w PSU. I've run quite a few games, synthetic tests and 30 mins of Furmark and no problems at all. It's still at stock and I have a 3700x which is just using PBO so I guess I'm being careful not to overload on the power.
I think if you have a good quality 650/750w PSU you should be fine, unless you go over the top with other components drawing a lot of power.
2700X/16GB RAM/Gigabyte Gaming 3080 on a Super Flower Leadex Gold 650w 1st gen. Seems fine so far, did have one hang which eventually rebooted the PC but no idea what that was. What's the best/easiest way to measure power draw? Ideally when gaming to get some load going.