A power supplier of a computer system and a power supply method thereof are described. The power supply method includes the following steps, receiving a validation code when a computer system enters a working mode from a standby mode; determining whether the validation code is in accordance with a preset code; If the validation code is in accordance with the preset code, executing a power sequence control so that the power supplier generates a plurality of working voltages required by the computer system; and if the validation code is not in accordance with the preset code, powering off the computer system or keeping the computer system in the standby mode.