Low voltage transformer which are sometimes referred to as a step down transformer are used to convert main line voltage to a lower voltage suitable for bulbs. Transformers can be used with incandescent, halogen, xenon and krypton type bulbs.

This transformer has a "120 Volt" Input Voltage which is converted to "12" Volts. (AC)
Measurements 2.88" Long x 1.38" Width x 1.00" Height
This transformer is dimmable 

Minimum wattage requirements are common for lighting transformers. This means that the transformer will not produce 12 Volts if  the "20 Watt" minimum wattage amount is not applied. 

Always make sure power is off when working with electrical parts and fixtures.