My iMac G5 17" (with Ambient Light Sensor) would not start up yesterday, so I took it to the Apple Store and they believe the power supply to be bad. They would replace it but charge a lot for labor that I can do myself (I have already removed my power supply). I was wondering if I needed to match the same apple part number on my old supply as the new one. Or is it possible for me to just go out and buy an power supply that was in (or fits) an Ambient Light Sensor. Thanks for the help.