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.
In America, this name received a boost of popularity in 2000 when a character bearing it began appearing on the television series The West Wing.
As a given name, it was used on the American sitcom Murphy Brown (1988-1998) for both the mother and son of the main character. By 1998 it was more popular as a name for girls in the United States, perhaps further inspired by a character from the movie Jerry Maguire (1996).