Review on Black 24 Volt Transformer & C Wire Adapter for Ecobee, Nest, Honeywell Smart WiFi Thermostats, Ring, Blink Video, Nest Hello, Skybell, August Doorbell: Power Supply Compatibility by Richard Cunningham

I bought this product to enable me to use the Wi-Fi Smart Thermostat because I had an old 2 wire system with no common wire on the boiler control board. The smart thermostat requires a common 24VAC wire and this allows me to connect a 2 transformer configuration to the thermostat. Okay, I'm happy to report that this product allows my smart thermostat to work! Definitely positive! However, I was concerned that this would not happen and I think the product is not up to date. It is advertised as a 24VAC plug-in transformer but only supplies 23VAC. Luckily the thermostat still works with dispersion, but I still expect the output to be 24VAC. I'll probably switch it to a different brand later. I checked the output in the attached image from 3 different outlets and also tested them to make sure the input was 120ac, which it was, not that I was expecting anything else.