Hi,
A typical plug is rated at around 15 amps, or about 1600 - 1800 watts, depending on the voltage. I have never seen a inverter with separate plugs - at least something that small wattage wise.
The second plug is only there to make it easy to plug in two items or two extension cords, ect. You should not exceed the rated capacity, but can use the full rating from either plug, or split the load anyway you like between all of them.
There are a lot of hardwired inverters, mainly rated more than 1,000 watts that would not follow these abilities. Some inverters in the 3,000+ watt range might have 120/240 output, with different rules and/or capacities.
Fred.
