Most, if not all, of Cisco's stuff (at least the rack mount stuff)can be ordered for use with -48vdc, which is a telco standard.

I believe it's as easy as swapping the power leads (plus becomes minus, minus becomes plus or, 48vdc becomes "zero" and the negative lead, relative to the positive lead, is -48VDC)).

For some devices, the power supplies are swap-able from AC to DC, for most of the one RU devices, I believe they have to be ordered as DC devices.

Make sure your power is properly filtered and isolated ...

Good Luck

Scott