A doorbell transformer is a small step-down transformer that converts 120-volt household power to the low voltage, usually 10 to 24 volts, that runs a wired doorbell button and chime. It is typically mounted on a junction box near the panel, furnace, or chime, and is rated in volts and volt-amperes (VA), which video doorbells often need more of.
Why it matters to you
When a wired doorbell goes silent, the cause is usually a failed button, a loose low-voltage wire, or the transformer, and an undersized transformer is a common reason a new video doorbell keeps rebooting or dropping offline.
Practical guidance
Check the button and chime wiring first, since the low-voltage side is safe to handle. The transformer's 120-volt side connects to household wiring, so turn off its circuit breaker before touching it, and match any replacement's voltage and VA rating to the chime or video doorbell maker's specification.