A power supply circuit for a CPU (central processing unit) includes a CPU, a power supply, a plurality of voltage adjustment modules, a pulse width modulator, a plurality of resistivity selection modules, and a module management unit. The resistivity selection module includes an electronic switch, a first resistor, a second resistor, a third resistor, and a fourth resistor. When the CPU operates abnormally, the power supply circuit utilizes the resistors in the resistivity selection module as voltage dividers, thereby restricting MOSFET or other components to operate in a normal voltage range.