A power supply circuit includes a first resistor and a first capacitor. One end of the first resistor is connected to a system power. The other end of the first resistor is connected to the anode of the first capacitor. The cathode of the first capacitor is connected to a digital analog converter A (DACA) VDD pin of a north bridge on a motherboard. The system power provides a stable power signal for the DACA VDD of the north bridge via the first resistor and the first capacitor. Thereby the display no longer ripples when the resolution of the display is adjusted to a certain value.