Reduced load capacity in a switching power supply may have the following causes:

1. Ageing or damaged components: switching devices, regulators, filter capacitors and other electronic components can deteriorate over time, reducing their ability to provide enough current or voltage for heavy loads.

2. Overheating: prolonged high-load operation can cause overheating, especially with insufficient or faulty cooling. High temperature affects component performance and reliability and can reduce load capacity.

3. Control-loop problems: the control loop monitors and regulates output voltage and current. Problems may amplify errors or prevent a correct response to load changes, reducing load capacity.

4. Incorrect overcurrent protection settings: protection safeguards the supply and load against excessive current. Overly conservative or sensitive settings may trigger protection even under normal loads and limit load capacity.

5. Insufficient power rating: in some cases the supply's own power capacity is too low for a heavy load. An undersized supply cannot provide the required current or voltage, resulting in reduced load capability.