The following methods can be used to reduce harmonic currents in a switching power supply:

1. Filters: Suitable filters can reduce harmonic currents at the output of a switching power supply. Common examples include LC and LCL filters. These filters remove high-frequency harmonic components, reducing harmonic current amplitudes.

2. Resonant circuits: Adding a resonant circuit to the output of a switching power supply can effectively reduce harmonic currents. Through resonance, the circuit can transfer harmonic currents to other frequencies, reducing harmonic currents at the output.

3. Modulation techniques: Suitable modulation techniques can reduce harmonic currents in a switching power supply. For example, PWM (Pulse Width Modulation) can adjust the on-time of the switching transistor to reduce harmonic current amplitudes.

4. Design optimization: The circuit topology and component parameters can be optimized during switching power supply design to reduce harmonic current generation. For example, appropriately selecting inductor, capacitor, and transformer values can reduce harmonic current amplitudes.

5. Standards compliance: Compliance with relevant electrical safety and EMC (Electromagnetic Compatibility) standards is also an important method for reducing switching power supply harmonic currents. These standards specify harmonic current limits and requirements to ensure that the power supply does not generate excessive harmonic currents during operation.

Reducing harmonic currents in a switching power supply is a complex engineering problem requiring consideration of circuit design, filtering techniques, modulation methods, and standards compliance. In practical applications, these methods should be combined according to the specific situation to achieve the goal of reducing harmonic currents. Guidance from a professional power supply design engineer or consultant can also be very helpful.