I would not make my own powdered eggs.  Have you tried making cakes, brownies and cookies without the eggs at all?  We cook via an outback oven or nested pans to create an oven and typically will omit the eggs, add a very little more water and oil, and call it good.  I was once told that the eggs used in baking flour products are primarily to keep it together for durations longer than our typical dessert lifetime (a few hours max).  Sure, if I have powdered eggs, I'll add some to the mix, but I wouldn't sweat it.  Many people reduce the oil and use applesauce at home, but I don't want to take applesauce either.  Plus oil is good for lots of stuff.