The transformer's job is to equalize or to balance the input voltage to the output voltage of a device when the delivery of the input is different to the output voltage of the device.
The transformer also can balance and stabilize fluctuations of the electric power supply for devices having the same input and output so that the device always gets the constant power. The transformer is suitable for and works best with any sources for example CD player, DAC, pre-amp or turntable. Not recommended is it for driving with big amps.