In Britain the parallel form Alice, derived via Old French, has historically been more common than Adelaide, though this form did gain some currency in the 19th century due to the popularity of the German-born wife of King William IV, for whom the city of Adelaide in Australia was named in 1836.
The name was originally used among early Christians in honour of the saint, as opposed to the classical character. In England it was commonly spelled Ellen during the Middle Ages, and the spelling Helen was not regularly used until after the Renaissance. A famous bearer was Helen Keller (1880-1968), an American author and lecturer who was both blind and deaf.
Although this name was used by Jews in the Middle Ages, it was not typical as an English Christian name until after the Protestant Reformation, being common among the Puritans.
This name is borne by a Jewish woman in Walter Scott's novel Ivanhoe (1819), as well as the title character (who is deceased and unseen) in Daphne du Maurier's novel Rebecca (1938).