Well, after testing the power supply separately (I know it puts itself into standby mode without a load), and finding that it didn't even start to start up, then re-setting the PMU just to make sure... I HOPE it's the power supply.  No light at the power switch, even.  I don't know how to test it further.  I'm an experienced modder, but this power supply is a bit baffling to me.  If it COULD be something else, I'm open to suggestions!

Dual 867 MDD:
2BG RAM, 1.2 TB storage over 6 drives + 2 Pioneer 110 DVD burners
ATI 9800, Pinnacle DC30, ATI Rage128 pro video cards
Adaptec 29160N SCSI, Griffin G4port serial port

Modded 1.42 Gig Mini:
re-Built inside metal briefcase
3.5" 300GB IDE HD + 2GB RAM
DL SuperDrive
Bluetooth + Airport Extreme
built-in 17" LCD monitor
built-in Behringer F-control Audio I/O
built-in DV bridge w/ audio/video I/O

Dual 2GB G5:
2GB RAM + 1TB storage over 2 SATA drives
Pioneer 106D DVD burner
ATI 9800 XT & 9200 video cards
(4) 21" DELL P1110 monitors
Airoirt Extreme, FW800, all the usual...
Dual 867: 2GB/1.2TB/6 HD/2 110Ds/ATI 9800, Pinnacle DC30, Rage128 pro/SCSI/G4port ### Modded 1.42 Gig Mini:re-Built inside briefcase/3.5" 350GB IDE/2GB/DL SuperDrive/BT/AirportEX ### Dual 2GHz G5:4GB/1TB/106D/9800XT/9200