This came with a specific AC-DC Ring branded DIN rail transformer - 220V AC --> 24V DC (https://en-uk.ring.com/products/din-rail-transformer-gen-2) Obviously, the doorbell is compatible with both AC and DC, however, I want to make sure its not polarity sensitive on DC! EDIT-- I just found this statement on the installation instructions for the transformer that I didn't notice before: * Connect the doorbell wires to + & - (doorbell wires can go in either terminal). Which leads me to believe that the doorbell is polarity agnostic.

Hi @blademansw. For clarification, the Doorbell Pro 2 can be installed with an existing doorbell transformer within the range specified below, or the compatible Ring accessories below. **For connecting to an existing doorbell system:** - Hardwired transformer (16 to 24 VAC, 50/60Hz, 10VA to 40VA) **Compatible** **Ring accessories:** - DIN Rail Transformer (24Vdc, 420mA) - Plug-In Adapter (24Vdc, 500mA) Regarding the polarity, you are correct that the doorbell wires can go on either terminal as outlined in the instructions. Make sure the terminals are tightened properly with a screwdriver. If needed, you can reference the installation instructions [here](https://support.ring.com/hc/en-gb/articles/360054675132-Installing-Your-Video-Doorbell-Pro-2) as well.