A linear voltage generating device for testing performance of a power supply includes a comparator circuit, an analog to digital (A/D) conversion circuit, and an amplifier circuit. The comparator circuit is configured for receiving a pulse width modulation (PWM) signal, and comparing the PWM signal with a reference voltage to output a filtered PWM signal. The A/D conversion circuit is configured for receiving the filtered PWM signal, and converting the filtered PWM signal to a linear digital signal. The amplifier circuit is configured for receiving the linear digital signal, and outputting an amplified linear digital signal to an electric load electrically coupled to the power supply.