how does the mobile charger work?

how does the mobile charger work? they are too light. though they are rectifiers, they do not use transformers. (they are so light!) . i've heard that transformerless design consume lot of power and also they are dangerous. do they use any comparators or any other stuff like that?

They are usually switchmode, and do use a transformer - just a high frequency one - this makes them small and light.