Usually, although the newfangled inverter models do modulate down the power.
Relevant to this topic, the baseline time for the 50% can vary. eg my microwave does it in 15 second increments (ie 50%='450W' is 15 seconds at
900W full power then 15 seconds off; '300W' = 15 seconds on followed by 30 seconds off). If the thing in there is quite light, that 15s on time can be enough to boil it over or eggsplode it.Theo