General Nuisance wrote:
...I believe the way they lower the power (if I'm not mistaken) is by creating an electric charge with coiled wires. When the alternating current goes through the coiled wire, it creates an electric charge. Depending on how many coils there are in the wire, it can either lower, or increase the voltage (This is also how inductive charging works). I am not sure if it changes to DC through this process, or if that is done separately.
The sort of old-fashioned power supply you are thinking of has a transformer with two coils, one supplied with mains electricity and the other outputting a different, usually lower, voltage by induction (this is not a 'charge' - a capacitor holds a charge which can be discharged when required - induction only produces an output when there is an input). This is still an alternating voltage so it has to be rectified, usually with a bridge rectifier, to produce a voltage which swings zero to the output peak, rather than going positive and negative. A capacitor is then used to smooth out the peaks and produce DC. This is very primitive - for one thing the output voltage almost doubles when under no load (because the internal resistance - losses in the transformer - is then insignificant compared with the route resistance so the entire voltage is applied to the output rather than its being divided between the route and the internal resistance), so it's normal to use a circuit to regulate it to a constant voltage over a reasonable range of loads.
These are bulky and heat-producing; pretty well all modern power supplies and chargers are switched mode - for a detailed explanation of that please see https://en.wikipedia.org/wiki/Switched-mode_power_supply as already suggested above.
You (I think it was you) made a reference to a 'block' fitted to the USB-to-lightning lead. Older iPod leads don't have this, and it's probably a simple ferrite core designed to reduce RF interference picked up by the cable - it has no effect on DC, just damps AC at higher frequencies. It's certainly not a charger.
When connected a computer the voltage from the USB socket charges the device quite slowly. A proper charger is faster and should have a built in facility to detect when charging is complete - probably switching off until the battery has discharged by a couple of percent then picking up again.
