In a medium bowl, whisk together the marmalade, soy sauce, vinegar, garlic, ginger, and red pepper flakes. Heat the oil in a large skillet or wok over medium-high. In a ziplock bag, toss the chicken with the cornstarch, salt, pepper, and garlic powder to coat. Spread chicken in a single layer in the hot oil. Cook for 12-15 minutes, flipping every 4-5, until chicken is browned and cooked through. Pour in the sauce and cook an additional 2-3 minutes, stirring frequently, until sauce thickens and glazes over the chicken. Serve with rice.