Stir 1 cup sugar into the hot water in a large bowl until the sugar is completely dissolved. Soak the pecans in the water for 1 hour; drain.
Preheat an oven to 400 degrees F (200 degrees C). Line two 9x13 inch baking dishes with parchment paper.
Sift the 2/3 cup sugar, chili powder, and cayenne pepper together in a separate large bowl; add the pecans and toss to coat evenly. Spread the coated pecans in a single layer into the prepared dishes.
Bake in the preheated oven until the coating on the pecans are bubbly, stirring once, 10 to 15 minutes. Remove the pecans from the pans immediately and spread onto a counter or other flat surface covered with parchment paper to cool.