The tags associated with a voltage are back. SE discourages the deletion (burnination) of tags. The problem with these tags is they don't really define a group of questions well (a 5V tag could describe many many different types of circuits).
These had been cleaned up before, and they are back. There are probably a few hundred of these. I propose we create a new power-rail tag and merge them with that.
The other option is we could delete them, if we cleaned them and had a really good reason for deletion.