You will most likely need the AHT for your computer to fix the runaway fan issue. Some replacement power supplies do and some don't trigger the temp sensors to need recalibration. Just do a google search for the Apple Hardware Test for your computer to download it and burn to disk and boot your computer to it. I have had to use it on two out of three G5 Towers I have had to replace this past year. I had found the file image on free sites. sorry I do not have the site at hand for you.