1. Switching frequency: The operating frequency of a switching power supply affects its levels of radiated and conducted electromagnetic interference. Higher switching frequencies generally lead to higher radiation peak frequencies and require more stringent EMC design.

2. Power supply design: The overall design and circuit layout of a switching power supply affect EMC performance. Good design should consider ground routing, signal shielding, the use of filters, and other factors to reduce radiated and conducted interference.

3. Input and output filtering: Filters at the input and output of the power supply play an important role in EMC performance. Input filters can suppress high-frequency noise on power lines, while output filters can reduce noise and interference on output lines.

4. Grounding design: Proper grounding design is critical to EMC performance. A good grounding system can provide good common-mode and differential-mode noise suppression, reduce ground noise, and improve equipment immunity.

5. Component selection: Selecting suitable components and materials also affects EMC performance. Examples include low-noise components, shielding materials, and components that suppress high-frequency oscillations.

6. PCB layout: PCB (Printed Circuit Board) layout plays an important role in EMC performance. A proper layout can reduce mutual interference between signal circuits and avoid signal loops and antenna effects.

7. Environmental interference: Other electronic equipment and electromagnetic fields in the operating environment of a switching power supply can also affect its EMC performance. For example, nearby wireless communication equipment and sources of electromagnetic radiation may interfere with normal power supply operation.

8. EMC testing and certification: EMC testing and certification can assess the compatibility and conformity of a switching power supply. Testing in accordance with international standards and specifications can ensure compliance in a specific electromagnetic environment.

These factors are interrelated. Designing and controlling them is critical to ensuring good EMC performance in a switching power supply. Considering them together can reduce interference with surrounding equipment and systems while improving the power supply's own immunity.