Charles,
DPM doesn't look at the power consumption of an ESX server, but it looks at the CPU and memory load. "VMware Distributed Power Management (DPM) continuously optimizes power consumption in the datacenter. When virtual machines in a DRS cluster need fewer resources, such as during nights and weekends, DPM consolidates workloads onto fewer servers and powers off the rest to reduce power consumption. When virtual machine resource requirements increase (such as when users log into applications in to morning), DPM brings powered-down hosts back online to ensure service levels are met." See VMware vSphere VMware Distributed Resource Scheduler (DRS) for more information.
Robert