just like you I stumbled across the powering a second disk with the power-outlet named “FAN”. On Sunday, I gave it a try, risqued an old HDD, and you know what? It worked!
Still I don’t actually know what that four-pin power connector is supposed to be. Hmmmm … could it be that it has 2x GND plus 1x 5 Volts an 1x 12 Volts for a serious 3.5" Harddisk oder CDROM’s. Imagine that!!!
If that’s true, I’m going to put an SCSI-Controller into the pci-e Port and boot from Tape