How to test power output of 30 amp

Damdifino wrote:
I want to test the power output of my 30 amp plug on my house to which I connect my RV. Which two of the three holes should I put the probes from a multimeter in?

Assuming you meant "voltage" and not "power", as above- stick the probes into "hot" and "neutral"--mostly to make sure it is "120" and not "240"

If you want to know about the "power", now you need to check the voltage in a 15a receptacle in the RV while something is on, like the microwave. That "loaded" voltage will be lower. How much lower? is the question. If you are on a long thin gauge wire extension, this can be a real problem.