No Power at Doorbell

I have the pro doorbell, powered off the official Ring transformer. About a week ago it just stopped working. **I confirmed 120VAC on the primary leads, but there is zero output from the transformer on the secondary and obviously no power to the doorbell itself.** So I ordered a replacement transformer from Ring, and i'm still having the same problem. 120 V confirmed, but no power coming out. If it helps at all, the resistance on the primary side of the first unit is about 21 OHMs, haven't checked the new one. So not sure how to proceed...seems like it has to be the transformer? **Is there anything I'm missing that it could be, other than the first transformer failing and the second being bad out of the box?** **Also wondering if the doorbell unit itself developed a short and is killing the transformers. Anyone know how to test the doorbell itself with a multi?**