Easy steps:
- Take out the Mediator, accelerator & passtrough. Put then back. With this act you will remove any oxidation from the contacts;
- If above didn't do anything, put a power socket into the floppy power header on the motherboard. It will alleviate the current from the Mediator to motherboard.
200W is more than enough, even in a very expanded 1200, but those 200W AT don't have this output (average is 130W!). So, if you have Voodoo, TV-card, Sound Blaster and net NIC plus a Blizzard PPC (with or without BVision), buy a stronger PSU (350W "declared" is OK).