One of my older CPAP machines would run on either 12v or 120. Had two plug connectors, one for the 120 cord, and the other for 12V. The last two had an external brick that provided 12v to the machine. I bought one of the 12V adapter cords for the first one, and have used the machines on 12V ever since. At home, I have the Brick plugged in, and do not even take it with us in the RV. The adapter cord,(which is nothing except a wire) has powered all my machines directly from a 12V outlet installed on the side of hte bed. The two black things on each end of the cord are supposed to keep electrial noise from the machine from feeding into the 12V supply, but are more for appearance and regulations than actual function. As my machine iw on a shelf above the bed, I did have to extend the wire to reach it. I have two 12V batteries in our coach, and have run the cpap for two or more nights with no problem.