There is no real way to know that. Each drive may do different things and there is no one to keep the vendors accountable.
The enterprise drives will ensure that your data can be written to disk on power off with internal capacitors intended for this purpose. The consumer grade drives usually have no such guarantee and you are their mercy if their flush command implementation really does write the data to the media.
Your only way to know is to test the specific drives you intend to work with.