Is it possible to add credit to an account from a credit/debit/not a gift card?
Here's what you can do: you can have a gift card credit on your account as well as a linked credit card. Here's what you can't do: you can't only add $10 from a credit card to your iTunes account. But if you have a credit on your account now, and you link a credit card to your account, it will use all the remaining credit from the gift card first, then charge the remaining amount to your credit card.