The GPT-9803 is a 3-in-1 model capable of performing AC withstanding, DC withstanding as well as insulation resistance tests. This tester is built upon a high-efficiency PWM amplifier platform with AC 200VA maximum output capacity to impede the influence from the voltage fluctuation of the input AC source. This ensures a stable voltage supply for the GPT-9803. The GPT-9803 uses a combination of hardware and software controls to improve safety: A self-check is performed to make sure all the functions and operations are under normal condition each time when the tester is turned on; the Zero Crossing Turn-On design imposes the output voltage to always begin at the zero crossing of a sine wave to avoid the impact of surge voltage output; and the output voltage is automatically cut off (within 150?s) when abnormal output voltages have been detected or when the upper or lower current limits have been reached during testing.