The cost of powering my 3090 for a year is now more than the cost (RRP) of a 3090.
Even assuming literal 24hr/day usage at a higher, "factory overclocked" 450w sustained, at a fairly high $0.30/kWh that's $1200/yr. Less than half the retail price of a 3090. And you can easily drop the power limit slider on a 3090 to take it down to 300-350w, likely without significantly impacting your workload performance. Not to mention in most countries the power cost is much less than $0.30/kWh.
At a more "realistic" 8 hours a day with local power pricing I'd have to run my 3090 for nearly 10 years just to reach the $2000 upgrade price an M1 Ultra costs over the base model M1 Max.
At $0.36/kWh - card alone @450W ~running cost ~= RRP 3090 $1,499
Yes, can power it down to be more efficient, however, that effectively agrees with the previous comment that PPW matters.