I'm rather surprised to hear about A1200 problems.
Me too!
I bought an Escom model in 1997 and it is highly expanded and still runs flawles. But I immediatly understood a couple of things!! If your really going to expand it then you should put it in a tower and use that power supply. I have had a Micronik case but I then bought an Elbox tower because I liked it much more.
I recently bought a second hand Amiga 1200 revision 1 (early days 1200 even without clock port header). I expanded it with 3.1 ROM, CD-ROM via PCMCIA, Blizzard 1230-IV / 32MB and 4 GB Travelstar harddisk and it runs flawles on the original power supply!
If your going to get a 68040 or 68060 turbo card you might need another power supply! I think one from an A500/A600 will do!
Oh, and if you gonna use old stuff; really clean the connector from the A1200 where the turbo card fits good!
PS: I now have an Amiga 600 and Amiga 1200 standing next to eachother! Looks nice.