There are basically two types of powdered milk. There's a non-instant variety commonly used for long term storage and there's the instant variety you find in the grocery stores. I get powdered milk from the senior commodity program and I buy powdered milk too. Both of the types I use are instant variety. The brands I buy at the store are for drinking and the commodity milk I use for cooking. Why?
Well, there are two different tastes to instant powdered milk. It's how the milk is made that makes it drinkable for me or not. One way producers make powdered milk is by cooking it. Milk is dripped onto a very hot barrel device which evaporates the moisture from the milk. In effect it's cooked to remove the moisture. It works like an ice cream maker in that it scrapes the milk off in thin sheets. Cooking anything changes its flavor. The other way powdered milk is made is by spraying in a vacuum chamber evaporating the milk instantly. It has a more natural taste because nothing changes except the moisture is removed.
If you have trouble drinking powdered milk it may be because you don't like the cooked taste of the milk. I suggest you keep trying until you find a variety of powdered milk that suits your taste buds. For me the commodity milk has too much of a cooked taste so I use it only in my cooking.
I do drink powdered milk because paying from 4 to 6 dollars a gallon at the neighborhood store is a bit much for my budget. I had to train myself to drink powdered milk. I searched until I found one made without the cooking process. The box does not tell you what process is used. I added vanilla to the milk which masked the taste until I felt comfortable drinking just plain milk. Mixing powdered milk and regular milk doesn't work if you are trying to fool someone. Again, it's the cooked taste that sneaks in there. First find a brand that is not cooked then try mixing them together or add some vanilla.
Even if you just can't bring yourself to drink powdered milk, at least give it a try in your cooking.