Is your puppy fine when you change different food for him/her?

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My puppy just puked and he is acting very sick now :-( I bought him new food yesterday before the old was finished, it was same brand name - Purina but different formula. He had puked when he was little baby when we changed different food for him, but he would get used to it quickly. I bought it at Petco, I'm gonna go see if they can change it for me, unfortnately, I threw away the recipe yesterday... but they could check with my Petco card.. I don'tknow. ave anybody experienced this before? And do you think I can get different package of food if I bring it back without the recipe?