I think they have to manually insert all the mistakes people (might) make. Sometime I feel the need to report my spelling mistake as an acceptable solution because it is so obvious (to me) that I pressed the wrong button but then I realise that would just cause incredible clutter and a lot of debate about what might and might not be acceptable. Although some exercises do seem more tolerant than others.
There's a separate word for "charger", i.e., "un chargeur". However, I would not be surprised at all that in French, an adapter (which normally accommodates different kinds of plugs/receptacles) may also include a charger built into it. Be that as it may, it may be prudent to say "chargeur" when you mean "charger" and "adaptateur" when you mean adapter until you get a chance to verify it in situ.
They are really two different things. A charger will charge up a device and it plugs into one socket at one voltage (usually 110 or 220v) and puts out 5v or 12v to charge the device. An adapter is technically only something that allows one type of plug to be inserted into a different kind of socket.
Adapter is a more broad term, it could be the part of your charger you plug in, a piece to use an American plug in Europe, adapters are used in piping to go from different sized piping, and on computers to use older/newer plugs with older/newer cables, and many other applications as well.
A liaison in this situation is considered optional and a very high register, except when followed by a pronoun. http://french.about.com/od/accents/fl/How-to-Pronounce-Optional-Liaisons-in-French.htm