So no matter what PSU I choose i get the error The MSI B450 GAMING PRO CARBON AC ATX AM4 Motherboard has an additional 4-pin ATX power connector but the Corsair RMx (2018) 650 W 80+ Gold Certified Fully Modular ATX Power Supply does not. This connector is used to supply additional 12V current to the motherboard. While the system will likely still run without it, higher current demands such as extreme overclocking or large video card current draws may require it.