One year prior to my arrival a vendor had installed a generator and installed outlets in the server closet. The generator was exclusively installed to protect servers, however the previous sysadmin or vendor did not bother to split the power to the server so that it was connected to both the Grid and the generator. I reconfigured the setup for proper redundancy, ensuring uninterrupted power during outages and enhancing system reliability.
While this shouldn’t have to be on the list, I have talked with many individuals who did not realize that power should be split between different power sources, so for that reason alone it is some what notable.
This was not caught earlier while at that employer because the generator had not actually been used until that time.