It is 220 volt AC to 12 volt AC step down supply.
It is simplest power supply. It step downs 220 volt AC mains supply available in offices and homes to 12 volt AC. It utilizes a step down transformer to step down voltage that can be used for different purposes. We can use different watt transformer for different wattage output requirement. If we want 12 volt and 1 ampere supply then we will use 12 watt 12 volt step down transformer and if we want 12 volt and 2 ampere output we will use 24 watt and 12 volt step down transformer.
We can calculate wattage of transformer by using formula
P = IV
|is power in watts
|is current in amperes
|is voltage in volts
Here is an important and useful app for transformer wire gauge calculation and turn per volt calculation.