Thanks @drea.drechsler .
I worked out some numbers based on the ATX PSU spec, the EPS pin should deliver a maximum of 20A at 12v which equates to 240W. The Mainboard 24pin connector should support 12A for the 3.3V rail, 14A for the 5V rail, and 20A for the 12V rail.
On the 12V rail, my burnt...