An outlet with incorrect polarity is an outlet you shouldn't trust. In a correctly polarized outlet, energy flows from negative diodes to positive diodes. Sometimes wires get crossed and you encounter reverse polarity, which can damage your electrical appliances. If this is the case with your outlets, you'll need to contact an RV technician or electrician. You can check the polarity of your outlets with a digital multimeter.
Plug the black lead into the middle input at the bottom of the multimeter and plug the red lead into the right input. Turn the multimeter on by turning the knob in the center to "Voltage AC."
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Insert one of the leads into the longer vertical opening in the outlet. This is a 0-volt neutral contact. Insert the other lead into the shorter vertical opening. This is a 120-volt hot contact. If a reading appears on your multimeter, then the polarity is correct because voltage is being transferred from the hot contact to the neutral contact.
Slide one of the leads into the hot contact and the other into the round opening. This is the 0-volt ground contact. If a reading appears on your multimeter, then the polarity is correct because voltage is being transferred from the hot contact to the ground contact.
Position one lead into the neutral opening and the other into the ground opening. If a reading doesn't appear on your multimeter, then the polarity is correct because voltage cannot be transferred between neutral and ground contacts, both of which contain zero voltage.