Combine the sugar and cinnamon in a small bowl and mix well. Set aside.
Heat the vegetable oil in a very large, heavy, deep pot or an electric deep-fryer to 360°F.
Fry the sweet potatoes, in batches, until golden, about 8 minutes. Drain on paper bags or on paper towels, sprinkle with the cinnamon sugar and serve hot.
Yield: about 20 servings