LOL! I guess it is unanimous to use the USB.
I sort of have the same setup but not factory. My Sable has a cigarette lighter but also a second outlet that is the same type as the lighter. I have a small 100 watt power inverter (your 120 volt line) that I can plug in if needed for something like powering my laptop if on an extended photo shoot or something. Sigh... If I ever get around to actually retireing as I intend I may actually get to use the danged thing on an extended photo shoot.