What's the difference between schizoaffective disorders and depression with psychotic features?

Depends on symptoms: A person who develops a depression with psychotic features will experience hallucinations and delusions only when they are very depressed. A person who has schizoaffective disorder will continue to have hallucinations and delusions after his/her mood improves and those symptoms can last for weeks or months afterwards.

Timing: Major depression with psychosis means that the person has no psychotic symptoms when they are not depressed. On the other hand, schizoaffective disorder means the presence of even subtle psychosis between episodes of depression or mania.