Ring Video Doorbell wiring connections

I have recently purchased the basic video doorbell (wired) and would like to connect it to a 24 volt direct current 0.42Amp, 10.0Watt transformer. As the output from this transformer is direct current there will be a positive and negative terminal. Looking at the back of the doorbell there is no indication as to which connection is positive or negative. How do I know which connection on the back of the bell do I connect the positive line from the transformer to? Thanks for any help.