An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source.
Basically this function goes like this; it decouples the circuits and then supplies the current from one circuit to another.
This transformer completely isolates all the circuits and then supplies power individually which makes it all the more desirable and comprehensive. An isolation transformer does not have a direct electrical path from the power input side to the power output side their design is based more on the requirements of the user. So, in a way you can say that they are customized transformers.