we do not know the psu power requirements of Blackwell gaming gpus yet (compatibility, socket etc). i would wait since they are coming in January (hopefully).
5090 will be 600watt so with a high end machine, 1000 watt minimum will be good. Aimin 80-85 load.
Sorry but, it is a terrible time to buy a nvidia gpu, probably 4090,4080 prices are inflated due to upcoming 5000 series. (i bought mine years ago for 1599$ 