If you have had problems in your motorhome with 12 volt cigarette lighter sockets not fitting the plugs on inverters, cell phone adapters or other 12 volt appliances, here is a good article.  There are actually 2 sizes of sockets and plugs.  Also, absolute maximum power should be less than 240 watts.  That is 12 vdc fused at 20 amps.  Most are fused at 7 amps.  Thus the largest inverter than can be plugged in is 240 watts if fused for 20 amps and 140 watts if fused at 7 amps
Cigarette Lighter Socket & Plug Info