Now, I'm trying to figure out why.
At the time when the second power supply was going, I realized one of my case fans was spinning slowly. And at the time when my first power-supply when one of my fans had stuck (not moving.) So I was questioning could a defective fan burn out a power supply? That seems unlikely to me.
Yes, it can. Anything that draws power directly from the PSU(which a case fan does) puts a drain on it. My guess is, if you're not seeing any smoke or scorch marks on the fan then it 'probably' isn't that. However, since they cost about $4 each (on the high end) might as well replace it and see.
I didn't know if anyone had any information on any parts commonly responsible for causing power supplies to burn out.
It's been my experience that when PSU's go out they go out from one of two causes: 1) Dirty power being fed into it. 2) A fault within the PSU that either through poor manufacturing or age has popped up and blown it.
Since you've gone through several, my suggestion would be that it's the power being fed into it. If you're not on a powerstrip, get on one, and don't scrimp. Get one with a built-in safety that will trip before your computer melts down.
Also I'd suggest changing outlets and getting the one that you've been using tested, along with the fuse-box that it's connected to.
Just some thoughts, before you blow a wad on a new box.