How to test old doorbell wiring compatibility?

I want to install a Video Doorbell 3 for a friend. Her house was built in 1980. I have not been able to find the transformer so far. The chime is on her wall. I have not tried to get model info off of it yet. For some unknown to me reason, she no longer uses that doorbell. Someone has removed the outdoor doorbell button and overlaid it with a doorbell button that transmits to a plugged in chime in her house. I assume that when I remove this current doorbell button, I expect to find the two wires that used to be connected to her original doorbell button. I would like to be able to test those wires to see if they meet the Ring Doorbell 3 compatibility requirements, as far as voltage, Hz and amps. So that I can safely wire the Doorbell 3 to those wires in order to trickle charge the battery in the Doorbell 3. I am not familiar with voltage/amp testers. Can anyone recommend such a tester please? Hopefully one that I can order on Amazon.

Hi @flashtivo. I recommend contacting a licensed and trusted electrician. They often are very familiar with homes in your neighborhood and can tell you where to locate the Doorbell transformer and if its power is adequate. I hope this helps!