I have an Ecobee power extender, never used. We didn't need it with our new thermostat, but you might. It doesn't come with Thermostat Essential or Smart Thermostat Lite.
It's this one:
https://www.amazon.com/ecobee-Power-Extender-C-Wire-Adapter/dp/B0DT9RCBGZ/ref=asc_df_B0DT9RCBGZ