I've read through the extension cord threads (thank you FlasherZ and others) and I haven't seen this addressed: Is it possible to carry one extension cord for infrequent 120V charging that could be used for drawing 16A when plugged into a 20 amp circuit and 12A when plugged into a 15 amp circuit? My thought is to have a 10 AWG cord made with 5-20R on one end and 5-15P on the other. It could be plugged into to either a 5-15 or 5-20 wall outlet. With the standard 5-15 UMC adapter it would draw the usual 12A when plugged into a 15 amp circuit. With the 5-20 UMC adapter it would draw 16 amp when plugged into a 20 amp circuit. Or does the 5-20 wall outlet only allow 15 amp if a 5-15P is plugged into it? Does the outlet act differently if it has a 5-15P or a 5-20P plugged in?