I have make a statement that a broken/shorted motherboard can damage a psu.
I kinda know it can be done because i have fried a couple psu over the years with some jackass stupid testing and accidents.
But i am simply not capable of giving a good explanation how this can happend.
Some other person points at this guide http://www.formfactors.org/developer/specs/ATX12V_PSDG_...
and says psu is broken by itself if it is broken because all security measueres should cover everything and simply shuts itself down if there is is any shorts, overloads, powerleaks between the diferent voltages etc etc.
But this is just a "guide" does the manufactors have to follow this.
Well that's a rather long doc. Short and to the point, it's not very common for a bad MOBO to cause damage to a PSU as most modern PSU have built in protection. Old PSU's I could see that might happen but once again, not very common. With all that said, is it impossible? No but very rare. The problem I would have in how it could happen is there are just too many variables to know how when and where. There's no way of knowing for sure.
Possible but not likely. Of course, if you put a motherboard with long soldering points into a cheap case with poorly made punch out brackets to mount it on then it's possible for the board to ground itself here and there and short out. It's more likely for a crappy PSU to damage a motherboard .