Those cigarette lighter plugs are really bad with high current draw. I have a Colman 12V cooler that I had plugged into a 110VAC/12VDC supply. It melted down the female socket on the power supply so I replaced it. When I plugged it in again to test it I noticed the plug getting very warm so I shut it off but I wasn't quick enough and the socket melted again. I'm pretty sure the male plug from the cooler was faulty and was causing the overheating so I cut it off and threw it away. When I hooked the wires up to a terminal block the cooler worked properly. I still haven't put a lighter plug back on the cooler because I just don't trust it any more. I suggest that if you are planning on using the cooler only on the boat that you cut the plug off the end of the chord and wire it to a terminal block before it sets fire to something.