What's the difference between 「～ておく」 と 「～てある」の動詞形？?

Question:

たとえば：晩御飯を作っておいて。
晩御飯を作ってあって。

Answer:

It's a difference of active and passive. ～ておく is used for active like when you are trying to do something.

On the other hand, ～てある is used for passive like something is being done. But your example with 晩御飯 is not so good because we do not say the latter so often.