Wired doorbells in your home are low-voltage devices. A wired doorbell transformer transforms the power from 120V to 16V so it may be used by your wired doorbell. Virtually all wired doorbells will use 16-volts, and most transformers are 16V. The wattage or VoltAmps is the difference between most wired doorbell transformers and you want to make sure your wired chime has enough wattage to serve the system. Having an undersized transformer will cause it to burn out.