The beefy workstation cards are 2 slots, but yeah the 4090 cards are usually 3.something slots, which is ridiculous. The few dual slot ones are water cooled.
I find it challenging to get my 4090s to consume more than 300 watts. There are also a lot of articles, benchmarks, etc around showing you can dramatically limit power while reducing perf by insignificant mounts (single digit %).