I purchased the AC200Max a year ago or so and soon will be using the RV 30A outlet. I’ve heard of a possible reverse polarity issue in this outlet. How do you check to see if this is a possible issue? I have a multi meter and know how to use it. I do have the proper voltage when probing the hot and neutral. When I probe with a stick power tester it lights up power at hot and neutral? Maybe it is sensing power close by the neutral? How do I check to see if neutral has power or not? I’m guessing I have to go to a known outside ground? I may be the missing the common sense check here. Maybe someone can enlighten me. Thanks
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This interface is the upper positive and lower negative.
Use a multimeter to connect the positive terminal to the positive terminal and the negative terminal to the negative terminal. The voltage is a positive value, there is no problem.
Also, on Amazon, one can find the NEMA-TT-30 Testers 
. There are many:
Journeyman-Pro 30/50 Amp RV - Portable Circuit Tester Analyzer Adapter, Male Plug w/LED Test Indicator TT-30 NEMA 14-50 (TT-30 (30 AMP), Circuit Tester (Male Only)) https://a.co/d/5GJ8sXc