Power supply ring 2nd gen

As a qualified electrician I have never seen so much information and conflicting advice as the for the ring video door bells. Anyways having realised my own original doorbell chime is not compatible I decided to wire the door bell directly. Can someone please tell me is it possible with or without a resistor( makes no sense) that I can connect directly to a power supply. Can someone also tell me what the minimum power supply spec is? I have seen a max spec WTF! Any advice please