What helps soften hair, and soothe skin best-supplements or shampoo?

 What are you feeding him; if you're feeding him a commercial diet you shouldn't be supplementing his food with extra vitamins; that can do more harm than good. How long has it been since you stopped feeding him food with chicken? It can take several weeks for the skin to recover and he may simply need more time for his skin to return to normal; it also takes at least a month for the benefit of fatty acids to show in the skin. The blood supply to the skin isn't as great as it is to other parts of a dog's body so it takes awhile for skin supplements to help. The shampoo and conditioner will help but they are a temporary solution to a nutritional problem. If you're certain your dog only has food allergies and not environmental allergies, and you're feeding him a well balanced diet,  the skin should improve; it just needs more time. Jessie is allergic to chicken but also has allergies to many pollens and some household allergens as well, and even though she gets allergen immunotherapy and is eating a food with an excellent fatty acid balance she periodically has a dry coat and dandruff. Lately she has had dandruff because of all the pollen. Allergies effect a dog's immune system in a variety of ways and it can be difficult to maintain a perfect coat all the time.

I would start supplementing with fish oil, Missing Link, or similar supplements.  I'm actually using one for my epileptic dog (there's something in Missing Link that triggers seizures for him) with an oil called Healthy Coat.  It's high in the Omega 3 &  6 fatty acids.  I have to say, I don't like that it's 1st ingredient is soy bean oil, but he's doing great on it and I do notice a big difference in his skin, especially the pads of his feet.

Eqyss also makes a fabulous product called Mega Coat Rebuilder.   I've used it on my powderpuff when his leg was shaved for an IV, and for other foster dogs who have had partial shaves for medical reasons.  It really does encourage coat growth & moisturizes the skin as well.

 Welcome to idog and thanks for the info about Healthy Coat and Eqyss.

Thanks, I've actually been a member for quite some time now, I just don't seem to get here as often as I'd like.

I might try the Mega Coat Builder for Jessie; she is doing great on immunotherapy but has dry coat and dandruff occasionally.