The Ring of Power is Maxmillian's Soul Jar
He really would have preferred keeping his original body after the full moon; but this was his backup plan. Julius's mind will eventually be overwritten. Conversely, the ring didn't do anything.
Max implies that being a ghoul will eventually result in said ghoul becoming a vampire in due time, perhaps in relation to how quickly they decay, and Julius simply completed the transformation faster than normal, it just happened to coincide with him putting on the ring.