FOR THE MARINADE AND SAUCE: Place chicken in 1-gallon zipper-lock bag; set aside.
Combine chicken broth, orange juice, grated zest, vinegar, soy sauce, sugar, garlic, ginger, and cayenne in large saucepan (with at least 3-quart capacity); whisk until sugar is fully dissolved.
Measure out 3/4 cup mixture and pour into bag with chicken; press out as much air as possible and seal bag, making sure that all pieces are coated with marinade.
Refrigerate 30 to 60 minutes, but no longer.
Bring remaining mixture in saucepan to boil over high heat.
In small bowl, stir together cornstarch and cold water; whisk cornstarch mixture into sauce.
Simmer sauce, stirring occasionally, until thick and translucent, about 1 minute.
Off heat, stir in orange peel and chiles (sauce should measure 1 1/2 cups); set sauce aside.
FOR THE COATING: Place egg whites in pie plate; using fork, beat until frothy. In second pie plate, whisk cornstarch, cayenne, and baking soda until combined.
Drain chicken in colander or large mesh strainer; thoroughly pat chicken dry with paper towels.
Place half of chicken pieces in egg whites and turn to coat; transfer pieces to cornstarch mixture and coat thoroughly.
Place dredged chicken pieces on wire rack set over baking sheet; repeat with remaining chicken.
TO FRY THE CHICKEN: Heat oil in 11- to 12-inch Dutch oven or straight-sided sauté pan with at least 3-quart capacity over high heat until oil registers 350 degrees on instant-read or deep-fry thermometer.
Carefully place half of chicken in oil one piece at a time; fry until golden brown, about 5 minutes, turning each piece with tongs halfway through cooking.
Transfer chicken to large plate lined with paper towels.
Return oil to 350 degrees and repeat with remaining chicken.
TO SERVE: Reheat sauce over medium heat until simmering, about 2 minutes.
Add chicken and gently toss until evenly coated and heated through.