In order to ensure a power supply is capable of meeting system requirements, how much should a power supply be rated over expected capacity?

In order to ensure the power supply is capable of meeting system requirements, it should be rated 30% over the expected capacity.

Explanation:

To avoid a system failure during the operations, it is advised that the power supply is rated 30% more than the actual capacity of the device. Moreover, in order to compensate for the loss of power that occurs during the transmission of power, i.e. through transmission lines, at nodes and junctions, in transformers, etc., it is preferable to rate the supply above 30% of the realtime capacity.