Usage of 3d printer hotend outside of printer
The power supply for the hotend in your printer may not have been able to supply as much power as your power supply.  It won't try to heat up too quickly because this can cause overshoot in the temperature.  It has no active cooling, so overshoot is very bad.  It may also be limited for safety reasons, or to prolong the life of the heater.
Once the hotend is at or even near the set temperature, the duty cycle is very low. This is because you want your idling power to be a small fraction of your total ability to drive.  This is so that the control system can quickly and accurately force the unit to stay at the correct temperature.