Rabbi Pinchos Bodner, in his sefer on Brachos, writes (based on the Shulchan Aruch (202)) that in order to make a hoadama on a vegetable (same for ha’etz on fruit) the item being eaten must either have the physical form or the appearance of the original vegetable. If the food item has neither the form nor appearance of the vegetable, a shehakol should be made. For this reason the Mishna Berurah writes (202:7) that the proper bracha on jam is shehakol, being that it has neither the form nor appearance of the original fruit.
Based on this halacha both popcorn and potato chips require a hoadama. In popcorn the kernels of corn are still intact and recognizable, and potato chips are clearly thinly sliced pieces of potato. However, corn chips which are made from milled corn, do not maintain the form of corn nor do they look like they come from corn. Therefore the proper bracha on corn chips is shehakol.
Pringles are a debateable issue. On the one hand it is made from dehydrated potatoes and do not retain the physical form of a potato and therefore should require a shehakol. However, R’ Bodner writes, that R’ Shlomo Zalman Aurbach paskened that since Pringles have the appearance of a potato after they are made from the dehydrated potatoes, a hoadama should be made.