I'm not sure what you're asking, and I'm not 100% sure if you are either :-) Some general information that may be helpful:
Power consumption needs to be metered at the distribution point (either via the CDU in the rack, or a meter in-line with the power cords) -- I don't know of any server hardware that reports power supply current draw, though I could be missing something.
"Power efficiency" is a fuzzy value for a virtual server as electricity usage is inherently physical -- If you must have a number for a specific VM your virtual machine could be said to consume 1/Nth of the power being drawn by the physical equipment hosting it (where N=Number of virtual servers hosted).
Note that this needs to take into account all supporting infrastructure (e.g. SANs) used in the virtualization environment, and even then it's an extremely rough value since it doesn't take into account what percentage of the load on the virtualization environment is created by a specific VM: It just splits the power consumption up evenly.
Relative efficiency of virtualized servers as opposed to the equivalent physical hardware is usually expressed as a power savings - The difference between the power draw of the fully-physical environment and the virtualization environment. If you never had a fully-physical environment you can estimate that value (number of virtual servers * average power consumption of a server).