Hot-Ground Reversed and Low Voltage Reading When Testing the 450W Inverter

I read "hot ground reversed " on my plug tester when plugging into 120V outlet. Also, when I use multi meter for reading I get 108V AC between hot and neutral, and when I read from neutral to ground I get 50V DC

The reason why there is a voltage drop across the Neutral to Ground is because the grounding terminal of the ac outlet is connected to the input section of the Electronic Ground Fault Protection Circuit on the power circuit board. Due to the above implementation, the Neutral voltage will be pulsing DC voltage with average DC value of up to 50 VDC with respect to the metal chassis of the ac loads / metal chassis of the inverter. This is stated on page 15 of the attached manual (p17 of the PDF). When measuring voltage of a modified sine wave inverter, reading will be 10-15% lower with a digital multimeter (DMM) that is not True-RMS. It can also be noted that the unit is a modified sine wave inverter so normal test methods for GFCI may not be applicable. The unit is certified for UL STD 458 electric standards which confirms that unit conforms to all electric standards.