Why Bus 0 Enclosure 0 power supplies are faulted during standby power supply (SPS) testing.
The primary power source is line power from the utility and the secondary power source is the battery. It is called a standby power supply (SPS) because the battery and inverter are normally not supplying power to the equipment. The battery charger is using line power to charge the battery, and the battery and inverter are waiting "on standby" until they are needed. When the line AC power goes off, the switch to battery power happens very quickly, but not instantaneously. There is a delay of a fraction of a second while the switch occurs, which is called the switch time or transfer time of the SPS. While rare, the power supply just knows that it is receiving DC power and reports an AC failure to FLARE/CM, which, in turn, reports this status to the Navisphere Manager GUI.
For more information, Refer EMC Knowledgebase article emc293424