If your laptop charger (or external hard drive or other electric device without battery) has a power indicator (led), then you can do the following experiment:
First, unplug the charger from the computer;
Then unplug the charger from the wall outlet;
Finally, observe that the led remains lit a few moments (sometimes 10 ~ 20 seconds), even completely unplugged!
How is that possible?
It is not magic or free energy, but science: in short we say there’s a bit of electricity in the power supply.
In this kind of power supply, the alternating current of the sector turned current continuous low-voltage (12 volts on mine).
Two steps are necessary: lower the blood to go from 230 V to 12 V and transform alternating current running continuous.
The second step is even divided into two sub-stages: aware is first straightened with a diode bridge, then the signal is smoothed to be practically constant and continuous.
History of the DEL takes its source in the smoothing: to get the current right smooth (good constant), using a large capacitor, which is here as an inertia wheel or the tank of a water dam: it allows to regulate the current, the same voltage at its terminals.
Its principle of operation, the electric capacitor stores electrical charges.
However, when we unplug the charger block, the capacitor is still loaded and it continues to deliver some electricity in the electric circuit of the bloc, including in the DEL, which continue to shine even if everything is disconnected