Substitute for potato flour for a cake

Does the recipe call for potato flour or potato starch? If it's potato starch, I agree corn starch may be a good substitute. Also arrowroot or rice starch. If it's potato flour, then that's a whole different beast, as it's typically used to help your finished baked good retain moisture and hold together. I can't think of an easy replacement without seeing the recipe first.

Potato flour should be acting as a thickener. I would substitute tapioca flour or any other very fine, absorbent flour like corn starch.

KKool, what type of cake is it? Tell us a bit more! A good substitute will depend on the desired outcome in texture, size and type of pan used.