ECC RAM isn't worth it for Plex.

Probably not.

Plex is a media streamer, not a database server. It doesn’t care about random bit flips. If a single bit flips in a movie frame, you’ll never notice. If it flips in a system file, the OS will handle it the same way it handles any other transient memory error — crash or reboot, which is extremely rare anyway.

On a 10-year-old DDR3 server, ECC RAM usually costs more and might be slower than standard unbuffered DDR3. Plus that server is already power-hungry and loud. You’d be better off spending the extra money on more storage or a newer, more efficient machine.

Future you will thank you for skipping the ECC and putting that cash toward something that actually improves your Plex experience.