The power supply for 3090 ti is one of the most important parts of your build. It needs to be able to provide enough power to your GPU and other components so they can work at optimal performance. If your PSU isn’t up to the task, it can cause a lot of problems and ruin your gaming experience.
Nvidia recommends a 750W PSU for RTX 3090 Ti as a bare minimum. However, overclocking your CPU can push power use up significantly and you may need more than that to stay safe. For example, Gamers Nexus found that the Asus TUF RTX 3090 Ti Suprim X consumed over 650 W at stock and overclocked.
Unlike the Founders Edition of the card, the OEM 3090 Tis feature a new 1x16-pin power connector that takes up less space than the 6+2-pin configuration. As such, they require an adapter that feeds three 8-pin PCIe power cables into the new connector (note: don’t use piggybacked power connectors on your PSU). MSI has included one of these with their 3090 Ti Phantom GS.
The RTX 3090 Ti is also the most powerful graphics card that Nvidia has ever produced, so it requires more power than previous models. A quality 850W PSU should be able to support the card and your CPU at stock speeds, while still leaving plenty of wattage for overclocking. Just make sure you get a PSU that has a continuous power rating rather than just a peak-rated number, as cheap ones tend to advertise the peak figure only.