Preheat oven to 200°F. Line a large rimmed baking pan with foil. Generously spray a large wire rack with cooking spray; place in baking pan; set aside.
Wash and dry citrus. Cut crosswise into ¼ inch-thick slices, removing seeds if needed.
Combine sugar and water in a very large skillet or small stovetop-safe shallow roasting pan. Bring mixture to boiling over medium heat; let thicken slightly, about 3 minutes. Add citrus slices in a single layer. Gently boil, uncovered, over medium heat for 8 to 10 minutes or until slices are translucent, turning slices over occasionally.
Transfer citrus slices to prepared wire rack in pan; discard syrup. Bake for 2 to 3 hours or until dry and leathery, turning slices over after every hour. Let stand on wire rack until cool and slightly crisp.
Line a large baking pan with parchment paper. Melt chocolate chips in microwave according to package directions. Dip one-third to one-half of each candied citrus slice into melted chocolate; let excess chocolate dip off. Place dipped citrus on parchment-lined pan. Let stand until chocolate is set. Store in single layer in an airtight container at room temperature for up to 1 week.
