Secondary or " Redundant B" Power is available in which case your servers with have access to a secondary UPS-  This option increases the SLA to 99.999 on power and in which case if one UPS failed your servers would remain online, if you have dual power supplies and have each one of them plugged into the secondary power outlet.

Secondary Power is recommended, that said most client do not request it.  Secondary  Power costs about 50% of the acutal power costs, and is there if and when you need it.