If he likes it, and you have some, I would certainly feed him that until it is gone.
Maybe he just likes variety? If he finishes off the Purina puppy chow, you could see if he likes the previous food again afterward.
Or maybe there is something specific about the puppy chow that he likes, and you might be able to find some other food that shares that thing. For example, since it's meant for puppies, it may have more protein and/or fat than some other foods, which might make it taste better to him. Or may it's a matter of beef flavor vs. chicken flavor vs. some other flavor. Or maybe it's how many calories per cup of food. He probably needs the same number of calories per day no matter what food he eats, but the food might taste better if the calories are more or less concentrated. Or maybe it's something completely different, that I haven't thought of.