A power supply apparatus for supplying an output voltage to a load is provided, which comprises a power output unit, a feedback unit and a control unit. The power output unit adjusts and supplies the output voltage to the load in accordance with at least one driving signal. The feedback unit dynamically detects output condition of the power output unit and outputs the corresponding detection result. The control unit determines a skipping ratio for an internal clock in accordance with the detection result output from the feedback unit, and outputs the internal clock with a part of the pulses being skipped to act as the driving signal.