Came across this on CL and don't have any idea what it is or what it's for. Perhaps someone can enlighten us.
http://sarasota.craigslist.org/rvs/1649652248.html
Oh yeah, because ads go away it's a Hughs Power Booster.

Danny,

This thing senses and boosts power at a campground if it drops below a certain voltage. Many electrical items, like a light bulb, will be OK with lower voltage, it will just glow dimmer. Many more electrical items, say a motor, require enough voltage to accomplish start up or they sit there and fry! Others like TVs can be erratic or damaged.

You can probably guess the problem now, you can't easily see if the voltage is too low or dropped in the night. So one of these rigs is there for that piece of mind....in exchange for a piece of your wallet of course

It's a voltage regulator. If the incoming voltage drops it will boost the voltage back up to a non damaging level. They usually give about a 10% boost.

I used to be a perm in a park with inadequate power. It got worse with higher occupancy and hot weather.

I used a Variac. This was before automatics. It had a wide operating range, but was not automatic.

This thing is known as a buck-up transfomer. I have sold a couple of these and have tested it using my generator load bank, it was very effective. Please note that if you are using an inverter, it can be adjusted to assume the load if you encounter a low-voltage situation. Ours is set at 105 VAC.