Question about giving my dog Benadryl?

I took my dog to the vet today for his allergies. The vet told me to give him half of a regular 25 mg benadryl. I went to the drugstore and they said that benadryl had been taken off the shelf so I bought the generic. It said compare to Benadryl Allergy Ultra Tab 25 mg. The ingredient is Diphenylhydramine Hydrochloride. I know that you're only supposed to give dogs regular benadryl, but did I buy the right one? I haven't given it to him yet because I wanted to make sure this was regular benadryl.