Combine the ketchup, chili sauce, tamari, ginger, and garlic powder and mix well. Pour ¾ of the mixture into a large food storage bag. Add the chicken wings, seal the bag, and toss several times to coat. Let the chicken wings marinate for 20 minutes at room temperature or for 4-8 hours in the refrigerator.
Prepare the grill for direct heat and preheat to medium. Oil the grates.
Using grill tongs, remove the drumettes from the bag and place on the grill. Discard the marinade. Cover and grill for 10 minutes. Brush the drumettes with the reserved marinade and flip them over. Brush the top side with more of the reserved marinade. Cover and grill for another 10 minutes. Give the wings a final brush of the marinade and flip and cook for another 1-2 minutes or until done and nicely charred.
Place on a serving platter, sprinkle with the green onion and sesame seeds, and serve with the ranch dressing on the side.