Yes, you should connect the additional ATX 12V power connector.
Yes, you should connect the additional ATX 12V power connector.
Yesterday I completed a build using a B550 Phantom Gaming 4. I connected the ATX 12V Power Connector (2x4), but recently I found an additional 12V Power Connector (1x4). Should I still use it now? Does it remain for future overclocking? The manual advises connecting the ATX power supply to this connector. I also have a picture of the manual. Thank you for your assistance!
It's for when you require additional strength to open, yes—I had motherboards with two extra connectors and I only ever used one, so it's fine.
ASRock guide appears to lack details, but I recall a motherboard manual suggesting you can skip the second or third CPU ATX12V when using low-power CPUs (like 65W or less Intel chips from Sandy Bridge to Haswell). If it's a third CPU ATX12V, it's probably for overclocking. From an EVGA manual example. I don't know your CPU model, but as long as it boots, it should function. Just avoid excessive overclocking.