Voltage drop if power draw is too quick: Does it happen naturally or regulated?
Laptop chargers seem to use the flyback principle. That is: The voltage in the output capacitor is observed. Every time it seems to be too low (there's a drop treshold well below 1V, say 100mV) a new current pulse is injected to the output capacitor to rise the voltage back to the acceptable level.

Injecting a pulse is a two phase operation:


a switch lets an inductor to accumulate current from the rectified mains voltage
the switch is turned off, the inductor current continues where ever it founds a way (it will make the way by rising the voltage until insulations break, if the route isn't prepared). 


In power supplies the prepared route is to the output capacitor which gets all energy which was accumulated to the inductor during the on-period of the switch.

This system has natural protection against overloading. Too high output current simply causes the output voltage to drop. Your guess "It pushes out max. 100W and drops the voltage if the current is too high" is not at all bad. The switch system cannot inject the pulses too frequently, accumulating the energy to the inductor takes time.

Flyback principle has a drawback. When the output current is low, the needed injections can be so sparse that the pulse frequency is in audio range. That can be heard because the inductors vibrate slightly. One solution is to observe the output current and make the injected pulses smaller to get a reason to output them more often, at an unhearable frequency. Direct current measurement is not a must. Smart controller can decide that now the injections are so sparse that they can be made smaller.

There's also another reason to observe the output current. A short circuit causes all injected energy to be dissipated inside the charger which will cause overheating. Again a direct current measuring is not a must. Indirect reasoning can reveal a short circuit. If repeating injections will not rise the output voltage high enough, the controller can decide "there's a short circuit" and halts the operation.