My puppy has similar problem. He has dandruff too. He was on Royal Canin puppy 33 and then I switch to Innova Puppy. But then, he has developed Staph infection after 2 weeks. Now, he is on antibiotics and we have to switch to another food with ingredients that he has never tried before. The dermatologist said that we have to try different food in order to rule out if the infection is due to food allergy or not. As such, he is on Natural balance Duck & Potatoes now for a few days. Still dunno if that would enable us to find out the root of his itchiness problem.
Will update you after 8 -12 weeks.