Are corrupted files after a power outage normal?

Don't go panicking thinking it's normal, because it really isn't. A power outage can corrupt files if your system was writing to them at the exact moment of the blackout, but it's not guaranteed and it's pretty rare with modern hard drives. The important thing is to check if you can recover them with recovery software, or otherwise check your backups if you have any. After that, an uninterruptible power supply or an external drive for important stuff is the investment that's worth it.