Worked easily.
I wanted to use both an Amazon gift card and a Visa gift card on the same purchase.  I also had to use a credit card to pay the difference, but Amazon considers a Visa gift card to be a credit card (and you can only use one credit card per order), so they suggested I add more money to the Amazon gift card and pay for it using the Visa gift card.  Worked easily.
Rating: 5 stars