I do not believe there is any command that list the power a switch or router is pulling from a wall outlet. Cisco documentation is the only place I know to get that information. If it is a modular device, such as a 6509, or even the 3750E switch with interchangable power supplies, you can use the "show inventory" command to get the power supply information, 750W etc. But you can find most of this in the data sheet for the specific device.
As for a formula to convert power, that all depends on how you want to represent the data, power can be measured in a number of ways, typically when you want to know the "load" you are pulling, or putting on a UPS (depends on perspective), you are typically talking about amps.
HTH,
Craig
