"adapter," "converter," "charger,"
What you call an AC adapter is usually called a charger because its purpose is to charge the battery on your Nexus. Back before I got grey hair we used to call a similar device (but way bigger) a power supply or power brick. It changes the wall voltage to 5 volts and makes it into the required Direct Current; it feeds it out the wire to a micro USB shaped plug.
The sort of thing that changes the physical shape of the plug so that you can plug your charger in the wall in Italy or other countries is commonly called an adapter. It doesn't do anything to the electricity except allow you to reach it when the prongs on your charger can't fit the shape of the outlet where you are.
A converter changes the voltage in the wall into the voltage your charger expects when you plug it in. If you had had a device which was expecting 110 voltage like in the US or Canada and you just plugged it into a European 240 volt socket you would see smoke, sparks, maybe flame if you are very lucky, and probably the circuits where you tried this would all be blown out. YOU'RE LUCKY, you won't have that problem. Your charger, as you have discovered, is usable across the spectrum and NEEDS NO CONVERTER. In fact, if you did plug your particular charger into an unnecessary converter all sorts of unpleasant things could happen there too. Don't do it. You don't need one.
All you need is a shape changer, called an adapter. Nice and cheap, get a couple in case you leave one behind. They're small, and that's easily done.
No sweat.