Great subject. Most household circuits are 20 amp. Take a look at your breaker panel. 20 amp circuits require, as previously mentioned, 12 gauge wire. Probably the lawyers would say no extension cord at all but the shorter the better and the larger the wire, the better. 16 gauge is smaller than 12.
You would think that there is no problem with a 16 amp max charger on a 20 amp circuit and there likely isn't; but what else is on that 20 amp circuit?
The margin can be improved by reducing the charge level through settings on the car. but here is always another BUT. If you use an aftermarket charger, it may not reduce charging current despite changing the car setting. You won't know without timing the charge or using a meter of some sort.
Has anyone found a cheap aftermarket charger that can be controlled by the car? I have a cheap Ebay one but am afraid to use it since my 20 amp circuits are 50+ years old, I haven't figured out what else might be on the circuit I use and the charger will only charge at 16 amps.