It's a receptacle outlet for which to plug in lamps, etc. However, it does have two receptacles (actually three: one double and one single), and I did need to flip two breakers to shut the power down for both; god am I glad I tested both receptacles. It appears to be the latter you described; two different power sources sharing a the white wire. The only grounding source there seems to be is the green screw on each receptacle, which are connected to nothing. Is this good info? Your help is much appreciated!