How did
Sauron get his strength (Parlty) back without
the ring?
He got his strength over (long) passage of time... 3000 years.. or something... until he managed to reform to physical form.
Not all of his strength was bound to the ring. Only best part of his strength. He has some power left in himself.
Also, Did Smegol ever wear the ring?
Of course.
At the beginning he was wearing it to steal stuff in his village, and to spy. Later he used it in cave to hunt
goblins for
food.
But he didn't used it to often. And he was pretty conformed in his cave, and didn't had a plan to ever leave that way of life.
This is why ring abandoned him.