i have an IMac a1311 without powersource and moatherboard 14 pin, i have atx powerboard used und conection voltage im pins like im picture used
[image|3511115]
[image|3511119]
then for that continuous 12v I used a 12v 400mA mini charger with a relay to have that continuous 12v and when the 250w atx power supply is turned on the relay switches that 12v to the atx power supply and when it is turned off the other way around like im picture below
[image|3511121]
[image|3511122]
[image|3511123]