A monitor device adapter includes first and second conversion circuits, a switch unit, and a monitor interface. The first conversion circuit includes a digital to analog (D/A) converter and a coupler. The second conversion circuit includes an analog to digital (A/D) converter and a decoupler. When the switch unit connects the first conversion circuit to the monitor interface, the D/A converter converts a digital signals representing data into a first analog form data for coupling with a first alternating current (AC) voltage. When the switch unit connects the second conversion circuit to the monitor interface, the decoupler decouples and separates a second analog form data into the second analog form data. The A/D converter converts the second analog form data into digital signals representing data, and outputs the digital signals representing data to the monitor interface.