Black box that allows just an A or B DC feed

I have a device that only has one DC power input. Is there a box that can accept an A & B DC leg, keep both isolated, & and feed my device with just A or B ? ie, if the A or B leg fails at the co-lo this blackbox will switch to what ever leg is up. Quickly, I hope ! Or are there other ways to solve this issue ? James Edwards Routing and Security Administrator jamesh@cybermesa.com At the Santa Fe Office: Internet at Cyber Mesa Store hours: 9-6 Monday through Friday Phone support 365 days till 10 pm via the Santa Fe office: 505-988-9200 or Toll Free: 888-988-2700