no obvious differences between these two. dei is often used in northern parts of china whereas people in the southern parts do not use that term to express the idea of "should" or "must".

在这种情况下，「应该」和「得」的关系与英语中的「should」和「have to」类似。

得 de； if you pronounce like "dei", it is more like spoken chinese (accento dialetto?)

They have no difference when used in a statement sentence. The mood of 'ying gai' is stronger and more formal than 'dei'. 'dei' usually used in the oral, and seldom used in a question sentence. btw: You need to learn how to write Chinese characters. Come on! ^_^