ypu can use a switching power suply. they are smaller, compared to the transformer and the circuit you will have and provide a better efficency.(i think so, they are around 80-90%. i am not sure, but i dont think that you get more than that by using a circuit with the transformer.)
also, the voltage is more stabilized, for the transformer you need a good secondary winding, because it might have a relatively big resistance so you will have a big drop on the maximum load.
or you can use a DC-DC converter, wich is almost the same thing.