the invention discloses a power supply with a frequency conversion function . the power supply is connected with a motherboard . the power supply includes a pulse width modulation controller , a direct current - direct current converter , and a switch resistor modulation circuit . the pwm controller generates a pwm signal . the dc - dc converter is connected with the pwm controller and the motherboard , and it generates a plurality of voltages to the motherboard after it receives the pwm signal . the switch resistor modulation circuit provides a first resistance value and a second resistance value switched to correspondingly generate a first switching frequency or a second switching frequency . the second resistance value is larger than the first resistance value . the second switching frequency is smaller than the first switching frequency .