It is a nice dream to have power consumption measurements built into IT devices (pc, laptop, servers, storago, and switches). The problem is this is not a high priority for any vendor and it will be done at minimal cost for development and production to provide a checkbox feature. This method is why wake-on-lan is so unreliable no one uses it once they figure out how inconsistent Windows and the devices are for this feature, and how different implementations from vendors cause frustration for users.
Power management as much as we would all love it to be built in to devices is going to be inaccurate an inconsistent. The google guys say they measure power consumption of their servers by tracking the cpu utilization <link>.
But, I think a more elegant way is to measure the power consumption on in a labo and a sampling of production units while collecting data from Windows Device Manager on an inventory of enumerated devices while collecting performance monitoring data for cpu, IO, RAM, monitors, and other power consuming devices.
Closed loop feedback systems are one of the architecture methods I use to think about whether systems have been thought through for how the system provides data on its operations.
Closed loop feedback is a well proven technique, but surprisingly is not used much in IT systems.