potato starch

I just bought a package labeled Potato Flour in a Chinese grocery, but I am sure that it is really the starch. The give-away is that if you press against the package, you feel/hear a squeaky-ness of the starch.

No, they're quite different. Potato starch can be fully substituted for tapioca starch (which is also called tapioca flour, I know it's confusing) and vice versa. Potato starch and corn starch are interchangeable as well, but that works better for quantities 1/4 cup or less. Potato flour is less starchy (go figure) and more gummy, so it cannot be used in place of potato starch. If you can't find potato starch, I'd use tapioca starch or arrowroot powder, or corn starch in a pinch.

This answer is from Ener-G, the egg replacement people. "What is the difference between Potato Starch, Potato Starch Flour and Potato Flour?"

Potato Starch and Potato Starch Flour are the same thing. However, Potato Starch (flour) and Potato Flour are different.

Potato Starch is a very fine flour with a bland taste, that is made by removing the potato peel, made into a slurry and watery mix, then dehydrated to form Potato Starch. The Potato Starch is not cooked, thus it does not absorb much water unless it is heated. For example, it will make an excellent gravy if heated with liquid in a saucepan.

Potato Flour is heavy with a definite potato flavor made from the actual potato including the potato skin and will absorb large amounts of water because it has been cooked and contains the peel. It is not used as main flour in baking as it would absorb too much liquid and make the product gummy. Small amounts are used to increase water, hold product together and so on.