The short answer
Yes — cooked sweet potato is a nutritious, budgie-friendly food.
Why
Sweet potato is rich in beta-carotene (vitamin A), which supports feather and eye health. It must be cooked, since raw is hard to digest — and always plain, with no butter or salt.
How to feed it
Steam, boil or bake it until soft, let it cool, and offer a small mashed amount or a soft chunk.
How much & how often
A small serving a few times a week.