Voltage converter indicator. Close-up of a voltage converter power source indicator and on/off switch. This device is also known as a voltage transformer and can be used to increase or decrease the voltage of an electrical power source. This step-up/down converter allows the conversion down of 220/240 volts to 110/120 volts and the conversion up of 110/120 volts to 220/240 volts. This unit shuts off automatically when input voltage is out of range.