It could be just pure coincidence. Nothing exciting about hard drives dying at ANY point of time. If you are worried about the power coming off the wall then just get a PSU with line conditioning. They are a bit more expensive, but at least you will be much more safe than nothing at all.
Since you have an external hard drive as well, then it is not the PSU, as it only handles the internal hard drives.
If you want to prolong your hard drives' lives then just follow the simple rules of:
1) Do not move, vibrate or shock them while they are working
2) Keep static electricity away from them
3) Keep them at normal room temperatures (avoid excessive low or high temperatures)