While in an airport recently, I treated myself to a bag of plain potato chips (Baked Lay's) without reading the label first. They tasted a bit odd, and sure enough, the label said that in the 32 g of chips, there were 2 grams of sugar. I threw the rest of the bag away.
There is usually sugar in barbeque and "all dressed" chips -- read the labels! -- but what on earth could be the motivation for adding sugar to plain potato chips? It just baffles me. To increase the addictive qualities of the chips is the only reason I can think of.