Triple-slot is no doubt big, but some custom designs coming from Nvidia's AIB partners are rumored to feature 3.5-slot coolers and these will get TGP's well above the 400 W mark. Since these cards are using the 8 nm manufacturing process from Samsung, the power efficiency might prove a bit subpar compared to AMD's Big Navi produced on the TSMC's 7 nm nodes.
https://www.notebookcheck.net/Leaker-shows-massive-triple-slot-NVIDIA-GeForce-RTX-3090-Founders-Edition-card-reveals-possible-RTX-3000-series-pricing.489285.0.html