In this article, Scott Whitney explains how to avoid getting put in a bad situation when you have to figure out how to choose a data center, and points to power as one of the main considerations:

Power is one of the main reasons to go with a data center instead of the "host it myself" plan. It is obviously crucial to the proper operations and uptime of systems, and there's an awful lot to know about it in order to keep systems up and running 24/7. The network operations center (NOC) manager should be able to speak fluently about power requirements, loads, circuits to your equipment, uninterruptible power supply (UPS), power distribution units (PDUs) and so forth.