Ive seen A1200 mobo's fried from just the BVision/BlizzPPC (esp 040 version) and a few mobo add ons that draw power from the motherboard when people have simply used either the floppy port or the original connector to power the system.
You need to feed your 1200 mobo from both in parallel IMHO. Its kept mine from frazzling OK.
As for something like the GRex etc, that should definately be powered independently of the 1200 motherboard!
