Scrub sweet potatoes and cut into 1/2-inch thick slices. Cut in halves or quarters if very large.
Fill a frying pan with 1-inch of oil and heat over medium heat until it reaches 350°F or a cube of bread browns in 30 seconds.
Fry sweet potatoes in the oil, being careful not to crowd the pan, until slightly tender but still firm, about 2 minutes. Remove to a heat-proof bowl.
Combine sugar, salt, cayenne powder, and water in a small saucepan and bring to a boil over medium-high heat, stirring until sugar dissolves. Continue to boil, undisturbed until dark brown and thick, about 5 minutes.
Pour caramel over sweet potatoes and stir to coat. Transfer to a platter and sprinkle with sesame seeds, serve immediately.