Inclusion of a Wifi radio substantially increases the amount of power the thermostat will consume compared to a typical non-wifi programmable thermostat that will often be powered by a replaceable battery.
You didn't state how many wires lead to each thermostat.
Ecobee include a Power Extender Kit (PEK) device with each thermostat, but at least 4-wires will be required between each PEK and its corresponding thermostat.
Honeywell offer a similar C-wire adaptor as an accessory, but the list of included items does not specify an adaptor being included with Honeywell smart thermostats.
Google Nest offer a 2-wire adaptor that also does not appear to be included, but it seems to offer less functionality compared to the 4-wire alternatives.
Ecobee PEK description
Honeywell Adaptor
Nest adaptor