If using active modules in the BCS chassis, like Telect's Ethernet Extension or DS3 repeater modules, Telect recommends connecting both A and B power connections for redundancy. Telect's BCS chassis that support active modules include a redundant power back-plane to help ensure maximum up-time for your active circuits.
If you are not using any active modules in the BCS chassis, one power source (A) is sufficient as it is only powering the DSX module's monitoring status LED. If the chassis were to lose "A" side power, the circuit would remain "up" as only the LED would quit working without the "B" side power attached.
