I HAVE THE SAME POWER, WHY DO YOU WANT TO CHANGE THE FAN? IF YOU CONNECT TO OTHER POWER SOURCE, YOU WILL LOSE FAN THERMAL CONTROL FUNCTION,THERE IS A 3PIN CONNETCOR FROM PSU TO MB,MAY HAVE SOMETHING TO DO WITH YOUR PROBLEM.
FOR OTHER PSU, I CONNECT IT TO A 4 PIN>3PIN+2PIN ADPATER.