doesn't the GVP HD8 sidecar need to be modded to close 4 jumpers to allow it to draw power from the A500?
my A530 (40Mhz 030/882, 8mb ram, scsi2ide bridge, 4Gb CF card) has a molex socket soldered to the PSU input, and a molex plug off of the floppy drive power port of the A500, and all runs off the A500 PSU. i havn't checked my HD8 yet, but since its PSU bit the dust, i havn't used it. especially since getting an A530.
at the moment, that very same A500 PSU is running an A1200 with a blizz1240 (40Mhz 040),scsi module, 128MB ram, elbox IDE flyer, 4Gb CF card.
so A500 power is not a problem :-) just from the sounds of it, getting it into the starboard is whats needed.
(and yes, paula does need the -12v line otherwise you get horrible crackly audio... which doesn't seem to be what it should be on all PC PSUs - seen a solid -4v on the -12v line. looked like no problems for the PC it powered, but for an amiga, diffferent story.)