Normally, machines will draw less than an amp or so, but as you add resistance to it, it uses more amps to keep running at the same speed. So resistance would be things like force applied to the skin, or ink getting into the cartridge or tube, or the different lubricants or creams we use to add moisture.
Power supplies are the median between them. They draw power from the source and limit it back to the machine. Some power supplies will allow more amps to be drawn than others. All of those things add up and affect how hard your power supply has to work to provide those continuous amps.