Nvidia recommends the following power supply wattages:
RTX 3090 : 750W
RTX 3080 / 3080 Ti : 750W
RTX 3070 / 3070 Ti: 650W
Note: Nvidia's recommended power supply wattages are based on a PC configured with an Intel Core i9-10900K processor.
We have many customers who do use an RTX 3080 with our NZXT H1, this is due mainly in part to their other components having a lower power draw than what Nvidia has calculated. We recommend you determine your total power draw with a Power Supply Calculator so you can verify if your planned system is compatible.