Mix sugar and cinnamon together in a small bowl; set aside.
In a large pot with a lid, heat oil over medium-high heat until hot, but not smoking. Add popcorn kernels and cover. When kernels begin popping, carefully lift lid and sprinkle in powdered sugar. Replace lid and continue cooking, shaking pot frequently, until popping begins to slow. Sprinkle with cinnamon-sugar mixture. Replace lid and continue shaking pot until popping has almost stopped (be careful not to burn). Remove any unpopped kernels.