make a binary_sensor that is on when above 300 W. Why care about 10W? Unless it can be on between 300 and 10w. And if that’s the case your logic is flawed and you need to re-evaluate what being on means. Anyways, here’s an example binary_sensor that will only be ‘on’ when above 300w.
or, use @petro ’ suggestion and add a delay_off option to it (which I need because the machine saves power during operation by switching between 3 and 200 watt for certain periods) Using the delay_off for let’s say 10 minutes would suffice.