I think I used a A500 PSU for my a1200 back in the day.
But remember having problems when installing a 060 turbo-board & 3.5" Harddrive. The PSU couldnt power it.
So if you plan to upgrade it with turbo-board and HD, you can get hold of a cheap PC PSU and get
this.
Or just make one your self. Google tells you how ;-)