If the outlet is on the left wall just in front of the rear seat
(mounted low) and looks like a household outlet it is probably the
factory setup.

The "switch" adjacent to it on a separate wall plate is supposed to
be a 110v circuit breaker.

The factory setup:
The 110v outlet has no power unless you are hooked up to shore power.
The circuit breaker may be broken, sometimes you need a pencil head
or similar to press in the reset button.

However, if a previous owner modified things who knows what you have.

Best to get a cheap mulitmeter and as others have suggested, poke
around and measure voltages.