Well having done it myself, I'm going for: bad HS and CPU seating.
Personally I would try reseating the HS on the CPU.
I cannot see a couple of fans swops making your PSU trip out, they would have to be the straw that...... I think you may of experianced trouble with your PSU before their addition.
By the way AMD will not uphold warranties on CPU's were "paste" has been used, they insist on heat transfer pads being used. Dont supposed it is relevent regards your current problem, but I thought you may appreciate being aware of their position , if in the future you were to install an expensive CPU.