Reducing power consumption of a desktop PC

My current home server, a Raspberry Pi4 with 4GiB RAM is running out of memory and i wondered whether i could convert my existing desktop PC into a home server. The Pi4 with a SSD connected over USB consumes only 7.1W at idle and 9.9W at load. Before i replace the Pi with the desktop, i wanted to check if it could achieve low power consumption at idle.