How to spot different electronic devices?
It's much more likely your rice cooker has a significant in-rush current that trips the censor. (Pun intended) The 0.4kW value is once it has warmed up. Initially it probably gobbles up a couple of kW.

If you know how to wire stuff safely, or know someone that does, you may consider an Inrush Current Limiter. Or a suitable Uninterruptible Power Supply (UPS) might work.

NOTE: ICL probably will not work if the rice cooker contains smart electronics and is not just your simple electro-mechanical thermostat. When the power is applied by the electronics the ICL will drop the voltage to the whole cooker, and the electronics will likely reset. In that case you would need to install the ICL internal to the cooker in series with the heater coil.