 Switches in the MDS 9000 Family have two redundant power supply slots. The power supplies can be configured in either redundant or combined mode. • Redundant mode—Uses the capacity of one power supply only. This is the default mode. In case of power supply failure, the entire switch has sufficient power available in the system. • Combined mode—Uses the combined capacity of both power supplies. In case of power supply failure, the entire switch can be shut down (depends on the power used) causing traffic disruption. This mode is seldom used, except in cases where the switch has two low power supply capacities but a higher power usage. In your case (assuming its a 9513)  Cisco MDS 9513 Ports Typical (Watts) Max (Watts) 192-ports 1,397 1,552 384-ports 2,097 2,408 528-ports 2,622 3,050   Thus you have options to choose from various combination of voltage and connectivity. First you need to decide what voltage are you going to provide. For maximum power you will have to connect it to two 220 volt supplies. The table listed earlier does hold good, and the logic for two connections is when we have a lower voltage power supply. The logic given by hersh holds good. However you may see that the switch would even run with single 220 volt AC connection, which will still provide 2900 watts. Though I would also suggest you to go with the recommendations of connecting both the power connections with same PDU.
I am looking at Cisco MDS 9500 AC power supply connections. There are two power supplies and each power supply has two AC connections. I am looking at MDS documentation and it's not clear if you need to take two connections from a power supply and plug them in to one PDU or if you take one power connections and connect it to PDU 1 and take second connection and connect it to PDU 2 ?  [IMAGE]  Any idea ?  Thanks
MDS 9513 and AC power connections