One of the better ideas is to get an AC voltmeter that plugs into a regular outlet. Watch the voltage, and if it stays well into the green, run whatever you need to. Even on a 50A circuit, if the voltage drops, cut your load and see if it comes up. That is the best indication you can get. If voltage is less than 120V, think very seriously about trying to run you AC or microwave. Those are the most sensitive to low voltage. Just because there is a 50A plug and breakers, doesn't mean that 50A is available. Depends on the wiring, and the load on that wiring. We have been in one campground that had 50A hookups and wiring, but the supply was only 115V. We had 50 amps of it, but still couldnot run the ACs.