One half of the 4+4 EPS12 connector is a mirror image keying of the other. If you put the two halves from the PSU together, you see the following pattern:
TAB
XOOX
OXXO
X are square-keyed pins, O have clipped corners on their bottom edges, makes them somewhat D-shaped.
If you have only a 4-pin connector, it will be the left half which corresponds to the legacy ATX12V pinout and keying. Only the correct half will fit without a fight.
Thank you.
I plugged the left half in and it all works well.
Now, I'm just having issues with the M.2 SSD not being recognised in the BIOS.
SSD: WD Blue 500 GB M.2 non NVME. I actually asked for SN 550 NVME one from WD Blue, but the provides sent this by mistake(The SSD fits snugly, but has 2 notches, while the slot only has one. That one fits perfectly).
But, I assumed it would still work, just for testing purposes, but it didn't. I'm not sure, if the same issue will occur when I replace this for the NVME. I'd appreciate any advice, if you know about that stuff as well.
Thanks again.
PS: The SATA HDD I was gonna use as secondary works fine, if that is relevant.