Convert kW tot Watt

Configuration
6

Nope. That’s not where you put it.

Put it in your configuration.yaml file. You should see a line that says sensor:

Put it all under it like this:

sensor:
  - platform: template
    sensors:
      dsmr_in_watts:
        friendly_name: "Current Power Usage"
        unit_of_measurement: "W"
        value_template: "{{ states('sensor.dsmr_reading_electricity_currently_delivered')|float * 1000 }}"

Unless your sensor line looks like this (which I think it does by default):

sensor: !include sensors.yaml

Then you actually have to put the template sensor in your sensors.yaml file - without the first line (sensors:) like this:

- platform: template
  sensors:
    dsmr_in_watts:
      friendly_name: "Current Power Usage"
      unit_of_measurement: "W"
      value_template: "{{ states('sensor.dsmr_reading_electricity_currently_delivered')|float * 1000 }}"

After saving the sensors.yaml file restarting home assistant this will create a sensor called sensor.dsmr_in_watts that you can use in your gauge card.