I have a 80+ Gold Corsair RM 850. But I used a separate power supply, the Corsair CX 450 to power the 1660 Super and the PCIe riser that I used to connect it.
I didn't switch any power cables. Using 3 separate 8 pin PCIe power cables, same as before, from 850 W psu. The temps are fine too, in the 50-60 range.
Specs: Ryzen 5 3600, MSI MPG B550, Corsair Vengeance RGB Pro 4x8 GB, MSI Gaming X Trio RTX 3080, Samsung 980 Pro 1TB, WD Blue SSD 1TB
Let me give you some background. Everything was fine until today I tried to install my old gpu (MSI Gaming 1660 Super) into my pc at the same time as my current...