When I use power calculator (www.cisco.com/go/powercalculator) to calculate the power supply needed for a 6500 (e.g. 6509E) switch. If I use a sup7203B with 4 x WS-X6748-GE-TX (with DFC3a), 1 x WS-X6704-10GE (with DFC3B) and 3 x WS-X6748-SFP (with DFC3A). The result display that the total power is 3323.88w and need a 4000w primary power supply. But the strange thing is, the result also display:
First Alternative Power Supply
So that means I can use a 2500w power supply as secondary power supply? or means that I need to use 2 x 2500w power supply? if I use 2500w power supply, what happen if 1 x 2500w power supply fails?