Dont know about UAL specifically, but that sounds like the electric outlet for the cleaners to plug in their vacuum cleaners etc. The outlets are on the ground handling buss from external power or the Nr 1 APU generator, and therefore not usually powered in flight. Not to say they couldn't be, just that 747's I've worked around weren't configured that way. Its 115 volt, 400 freqs power so I dont know how it might react with a 110v/60cycle transformer.