There is a show on youtube that I subscribed to. Some teens from France make all kinds of inventions and innovations in their show called “Incroyables Expériences”.
Their last entry (from 5th August) impressed me, they created something really useful: a handheld generator that produces 220v using a dynamo, excellent for emergency situations. You might be puzzled how this can actually work( and you don’t see this kind of stuff everywhere to be honest), but I’ll explain in a bit.
Here’s the video:
I’m not going to detail here, because curious people will look further and search about it on wikipedia and google. They used a transformer( ac adaptor). When this transformer is put in the right way, it transforms the 220v Ac current to whatever it is specified on the transformer case. But if it is inverted, it amplifies the voltage( the amperage is lowered).
Well, they didn’t make any breakthrough discovery, but they did show a very good example how this principle can be used in practice.