Originally Posted by jamman
At most 15 amps and more likely limited to 10 amps - x12 gives you 180-120 watts, assuming perfect efficiency. In other words, not much of one.
I agree, but that's still enough to run any laptop power supply (if you don't just use a direct from 12VDC supply), and a few USB power supplies or small battery chargers, all at the same time. No toasters or hair dryers...
I have a small (around 200 watt?) inverter in our van, and although it complains about low voltage unless the engine is running, it hasn't had any other problems. We have used it to run stuff such as camera and computer battery chargers - and a small heating pad - while driving.
DC outlets in cars are often marked "12V DC 120 W", suggesting a maximum draw of 10 amps and thus a bit less than 120 W (depending on battery voltage) of AC output.