Switching power supply output capacitor
If output capacitance is too large the power supply may shut down due to excessive charging current. This can affect supplies which have an over-current cutout. If the controller has a 'soft-start' function then you may be able to tune it to the higher capacitance.

Supplies which provide constant current or fold-back current limiting should work with any amount of extra capacitance, but the startup time will be longer. This might affect loads which need a fast rise time for proper initialization. 

Some controllers rely on a minimum amount of capacitor ESR (Effective Series Resistance) for stability. If you increase capacitor size or add capacitors in parallel the ESR could become too low. For example the LM2575 requires at least 0.05&ohm; to guarantee stability when running in continuous mode.

If you have a problem with voltage spikes during load current variations then you should add capacitance as close to the load as possible. This improves the effectiveness of the capacitor, while the resistance and inductance of the wires between it and the power supply provide some isolation.