I've never heard that one. It has many more characteristics of a modern urban legend than the simple "janitor unplugs the server then plugs it back in" story. Urban legends are essentially modern day folk tales. They'll often involve fear, horror, or even humor, and they're frequently cast as cautionary tales. They tend to be reasonably detailed (which helps keep a listener's attention), but at the same time they frequently not pinned down to a specific time or place. They're almost always told as secondhand stories (e.g. it happened to "a friend of a friend"), and tend to fall at the edge of plausibility.

But, the key thing is that urban legends always reflect some sort of underlying societal belief or worry. "Janitor polishes off patients" is about the fear of death, and how it can come for anyone at any time, and there's nothing they can do about it. "Janitor unplugs server every night at 5" is probably more about the idea that strange things happen sometimes, but it usually turns out that there's a good explanation.