The motherboard and then 1 or 2 expansion sockets, for a total of 3.
3 x 450W for GPU (Nvidia says 4090 draws 450W-- I think they're lying and will wait for reviews to see the truth) and 500W for rest of system. Though that might be a bit low, the 11900K has been measured at what, 300W under load? And you'd need a budget for USB-C power, multiple NVMe, fans, and whatnot. Maybe the spec would accommodate high-core-count enterprise processors so 600W+ would be wiser.
Even in euroland 2KW, which is what a maxed out system would be at the wall socket, is a bit much. They don't even allow vacuum cleaners over 900W to be sold.
2kW isn't actually that much — you can buy ATX power supplies up to 3.5kW for usage in 230V countries. Often used for mining, but also useful if you want to accelerate your blender renders by just throwing multiple GPUs at the task.
So, you expect GPUs to take 1500W of power, each? (230V @ 16A)