A switching mode power supply for an image forming apparatus, the switching mode power supply comprising: a converting unit arranged to convert an alternating current voltage input to the switching mode power supply to at least one direct current voltage by using at least one transformer; and a voltage controller arranged to control a voltage level of an output voltage of the switching mode power supply to be output to a system controller of the image forming apparatus from among the at least one DC voltage, where the system controller controls operations of the image forming apparatus, wherein the voltage controller comprises a switching unit to switch the voltage level of the output voltage from a first voltage level to a second voltage level when the image forming apparatus enters a power saving mode, where the second voltage level is lower than the first voltage level, wherein the voltage controller further comprises a voltage stabilizer including a voltage regulator connected in parallel to an output terminal to output the output voltage, and at least one resistor connected to a reference voltage terminal of the voltage regulator, wherein the switching unit is connected to the reference voltage terminal of the voltage regulator and characterized in that the switching unit comprises a diode through which current flows or does not flow based on a voltage of a control signal received from the system controller via an input terminal and wherein the switching unit comprises at least one resistor connected in series to the diode, wherein the second voltage level is determined according to a resistance value of the at least one resistor and the at least one resistor is a variable resistor, and wherein the system controller is configured to change the resistance value of the variable resistor to a resistance value to minimize power consumption in the power saving mode from among resistance values of the variable resistor. a converting unit arranged to convert an alternating current voltage input to the switching mode power supply to at least one direct current voltage by using at least one transformer; and a voltage controller arranged to control a voltage level of an output voltage of the switching mode power supply to be output to a system controller of the image forming apparatus from among the at least one DC voltage, where the system controller controls operations of the image forming apparatus, wherein the voltage controller comprises a switching unit to switch the voltage level of the output voltage from a first voltage level to a second voltage level when the image forming apparatus enters a power saving mode, where the second voltage level is lower than the first voltage level, wherein the voltage controller further comprises a voltage stabilizer including a voltage regulator connected in parallel to an output terminal to output the output voltage, and at least one resistor connected to a reference voltage terminal of the voltage regulator, wherein the switching unit is connected to the reference voltage terminal of the voltage regulator and characterized in that the switching unit comprises a diode through which current flows or does not flow based on a voltage of a control signal received from the system controller via an input terminal and wherein the switching unit comprises at least one resistor connected in series to the diode, wherein the second voltage level is determined according to a resistance value of the at least one resistor and the at least one resistor is a variable resistor, and wherein the system controller is configured to change the resistance value of the variable resistor to a resistance value to minimize power consumption in the power saving mode from among resistance values of the variable resistor.