The power supply controller is for use in a power supply circuit, for reducing acoustic noise. The power supply control circuit generates a control signal according to a voltage identification (VID) signal and a voltage sense signal, to operate a power switch in a power stage circuit, thus converting an input voltage to an output voltage. The power supply control circuit includes a conversion circuit and a PWM control circuit. The conversion circuit includes a DAC and a slope control circuit. When the power supply controller operates in an acoustic noise reduction mode and when a present level is higher than a requested level, the slope control circuit adjusts a descending slope of an analog voltage identification signal which is generated according to the VID signal, so as to restrain a decrease velocity of the output voltage to be higher than zero but not higher than a predetermined velocity.