For example if the transformer secondary is rated at 12 volts then the acquired 12 volts from the transformer secondary will be a 12 volt ac across the relevant wires.
Simple 12v power supply circuit without transformer.
We can convert the high voltage ac into low voltage such as 5v 6v 9v 12v dc without using the transformer which is called transformerless power supply.
It works by using a high voltage capacitor to drop the mains ac current to the required lower level which may be suitable for the connected electronic circuit or load.
Here is the circuit diagram and explanation for transformerless power supply.
And this series of works using capacitive reactance and resistance are not using this will reduce the heat on the circuit.
As the name defines a transformerless power supply circuit provides a low dc from the mains high voltage ac without using any form of transformer or inductor.
To be safe when there is a short circuit series always use a fuse on the input voltage is 220v.
The transformer is one of the main components in a power supply circuit because we need to convert the higher voltage available in the power point into a lower voltage we needed.
However for achieving a regulated dual power supply with the desired level of dual voltage at the output is something which normally requires a complex design using.