A resonance frequency adjusting circuit in electronic communication with a power supply and a load connected to the power supply includes a first LC filter, a capacitor, a switch, and a frequency detecting and control module. The first LC filter circuit is electrically connected between the power supply and the load. The switch is electrically connected between the capacitor and ground. The frequency detecting and control module detects a current transient frequency of the load, compares the current transient frequency with a first resonance frequency of the first LC filter circuit, and controls the switch to turn on/off according to the comparison.