Alrighty bud, been awhile, been quite busy. I brought the G4 home tonight to rip it apart.
First off, the computer has been sitting unplugged since my last post. I pulled the CUDA battery and tested it (good voltage), then waited 10 min, put the bat. back in, pressed the PSU reset button for a few seconds, then plugged in the power cord and tried the power on the G4.
The power button glowed when I pushed it, and I heard a faint "zz" for a split second, like something was shorting out. The red motherboard lights came on during that time, and then power light did it's pretty little fade to black and nothing else happened. I tried to press it again, but it seems as though it has a "cool-down" period, and I had to wait a few more seconds before I could get the faint shorting out/zz/click sound and the lights/etc. It happened even when the CD & HD were unplugged.
I grabbed a service manual PDF, did part of the PSU verification tests (got +25VDC on pin 14, +5V "trickle" on pin 1) but then when it came to the third step where I was supposed to power the machine on, it told me to replace the PSU since it didn't power on.
I pulled the PSU, and it's a AcBel API1PC36 unit. I've included a picture. No schematics on the 'net that I can find. What's next?