I’ve been using several Sonoff S20 plugs in my home for a while now. Their really great.
I re-flashed the units with Sonoff-Tasmota firmware to give MQTT support, this works really well:
Looking at the wiki it look like Sonoff-Tasmota supports Sonoff-POW and reporting power value to MQTT:
Once the data is in MQTT it’s easy to log to Emoncms. Either post to emon/<node-name>/<feed-name
MQTT topic and the data will appear in local emoncms (emonPi / emonBase) or just node-red to forward the data to Emoncms.
Node-red and MQTT are pre-installed and configured on all emonPi / emonPi. See MQTT user guide: