In my opinion the common use of these words are;
Adaptor: a Person who adapt to a certain situation.
Adapter: An inanimate object designed to adapt one thing to another.
I hope that in some way this helps.
Hello WF. Came upon this thread while searching for the difference between adapter and adopter.
Found a Bartleby link that said:
Adaptor is an infrequent variant spelling of adapter. Neither spelling is attached exclusively to persons or to things.
The only real difference is just the agentive endings of "er" and "or", of which, "American English has many such words, for which the suffixes seem almost randomly chosen."
I would have agreed with your initial definitions. But, I just looked up both words in 3 different dictionaries (not believing the first 2!).
Your Wiki definition is absolutely correct. For the device, one can use either adaptor or adapter.
BUT, for the person, the human being who adapts a novel into a filmscript or a a musician who adapts a composition for particular voices or instruments or for another style of performance, the only acceptable spelling is adapter (which is completely counter-intuitive). I would have bet that, like sculptor and actor, the -or ending suggested a person. But, instead, it appears to follow the "painter" model! Who knew?