Whisk 2 tablespoons curry powder, garlic powder, seasoned salt, onion powder, salt, thyme leaves, allspice, salt, and pepper together in a bowl. Add chicken and coat with curry mixture until curry mixture is wet and sticks to chicken.
Heat oil and 2 tablespoons curry powder in a large cast-iron skillet over high heat until oil is hot and curry powder changes color, 2 to 3 minutes. Add chicken to the hot oil mixture and reduce heat to medium. Add water, potato, carrots, scallions, ginger, and chile pepper to skillet.
Cover skillet and simmer until chicken is no longer pink in the center and gravy is thickened, allowing chicken to cook undisturbed for last 15 minutes of cooking, 30 to 40 minutes. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C). Remove chicken to a serving dish; continue simmering gravy, uncovered, to thicken (if needed). Serve chicken with gravy.