Anyway, it does seem that the CPU has a supply. What the stray might do is a mystery.
The numbers on the main connector have to be wrong on one of the pages.
The board has been rotated 90 left of course.
There is a similar sized 4 pin plug near the CPU, and showing 0,0,12,12v. So this will be the dedicated supply.
The stray plug is giving >3,12,5volts and ground off load. It would physically locate into the top four of the main connector. Again, I have no intention of doing so.
Just leave well alone, one thinks. But curiosity, and all that.
ISO 400 f14 priority - to give better depth. jpg problem? Still much better before it goes "through the Bucket".