Robotics: What is the maximum power of a robot? What is the minimum?

There is no maximum or minimum for the power of a robot.

Without saying what the robot is for, it's impossible to answer sensibly.

Some tiny toys & experimental ones take fractions of a watt.

Some big industrial ones take tens or hundreds of kilowatts.

There is no max or min.

Possibly soon, someone will build a billion watt robot, and someone else will build a nano watt robot requiring a scanning electron microscope to sort of see it.