To make the sauce, whisk together sugar, vinegar, ketchup, soy sauce and garlic powder in a large bowl; set aside.
In a large bowl, season chicken with salt and pepper, to taste. Stir in cornstarch and gently toss to combine. Working one at a time, dip the chicken into the eggs.
Heat olive oil oil in a large saucepan. Add chicken and cook until golden brown, about 1-2 minutes. Transfer to a paper towel-lined plate; discard excess oil.
Add chicken to prepared baking dish. Top with sweet and sour sauce. Place into oven and bake until the sauce has thickened, about 55 minutes, turning over every 15 minutes to evenly coat the chicken.