Can you fix power surge damage?

The simple answer is "Yes", but that answer also depends on exactly what happened to the hardware at the time of the power surge.

In many cases, replacing the power supply might be enough to bring everything else back up. However, if the surge was enough to send power beyond the breakers in the power supply, then the extra power might have gone through the devices connected to the supply, including the main system board, hard drives, etc.