This is a used transformer that provides 24v power. It can be used for a smart doorbell (like a nest doorbell) or for a 24v thermostat. I used it for a thermostat, but no longer need it. Details of the product are below:
No more doorbell/ thermostat underpower hassle:
24V 40VA Plug in transformer, replaces and upgrades underpowered transformer with this 24V transformer, offering plenty of power for your thermostats and doorbells.
Specification:
Input voltage: 120 VAC, 60Hz
Output voltage: 24V, 40 VA
Safe and stable:
Auto-resetting (PTC) fused secondary
LED green power indicator
Positive/negative/ screw terminals
UL certified: (E508012, Model PS-D40)
UL certification passed
Easy installation:
Electrical outlet mounting tab
Universal compatibility:
This 24v transformer is compatible with Ring video doorbell, ring video doorbell 2, Ring video doorbell pro, Nest Skybell doorbell, also compatible with Nest, Ecobee, Honeywell and Sensi smart thermostats, and other devices that require constant 24 volt power for operation.
Note:
The brand above is only for demonstrating compatibility.