Though this has been here a while...cannot hurt to add a comment.
If you are not sure the PSU has been damaged, use a diagnostics program like SiSoft Sandra. It has an environment monitor which you can use to review the running condition of your hardware, in this case, voltages and temperatures. Depending on your PC's internal monitoring capabilities, you should be able to determine quickly if the PSU is failing.
I recently repaird the parents PC after some supposed tech told them their mainboard was damaged. They consulted me after discovering just how much that would cost...mainboard, memory, CPU and vid card all would have to be done, which is costly. Pain in the ass when old hardware just is not available NEW off the shelf...I don't trust second hand hardware.
I am an electronics engineer by training, and the parents wanted my opinion. After taking an initial look, and wasting time replacing the caps (which the other tech was blaming the cause of the failure to POST), I was able to get the PC limping into the OS. Sisoft Sandra revealed a very eratic +5V standby voltage...as low as 1.5v up to 7 volts. Also, an intermittant hard drive failure at boot time was being reported, and SiSoft revealed that problem to be due to the +12V rail not up to par...it was averaging 11.2 volts with a registered low of 10.8V, well outside the 5% tolerance of most mainboards.
Though I do not blame a power surge, I do suspect the PSU simply had taken enough and could no longer hold it up. Newer components since the PC was put together, additional stuff as well...there are limits.
As for the comments about surge protection, I highly recommend a power conditioner. Surge protection devices are very limited in design and what they can do, and many do not survive a serious overload situation. It is mainly due to the varistors placed inside...they have a maximum voltage resistance...exceed that and it damages the device irreparably. Replace the power bar is the case.
A power conditioner on the other hand, is an active device that takes the AC power and through several different components, filters out surges and sags, essentially outputting a clean AC signal. It typically is not replaced like a basic power bar is, primarily because of the multiple components inside which are designed to take the punishment. They are costly, but are an essential device for places where power is not clean. Machine shops, welding shops, garages...construction areas...anywhere you need to have a PC (or photocopier which is primarily where I am familiar with them) is required to be reliably running.
A UPS is similar, but is a bit overkill in the price tag and size for a simple PC that doesn't require that much but is still in a problem zone.