Arnold
Said..
A transformer is a component that changes AC current from one voltage to another. A transformer consists of two coils, one connected to the input, and one connected to the output. A transformer can convert voltage up or down, depending on the number of windings on the coil.
An adapter MAY include a transformer to change the voltage, but an adapter usually changes the voltage AND converts from AC to DC as well, and may have a regulator that locks the voltage to prevent a surge and other components that prevent what is called "ripple".