Stir together 1/2 cup coconut milk, garlic, 1 teaspoon curry powder, brown sugar, salt, and pepper until the sugar has dissolved. Toss marinade with the chicken, cover, and marinate for at least 2 hours.
Bring 1 cup coconut milk, 1 tablespoon curry powder, peanut butter, chicken stock, and 1/4 cup brown sugar to a simmer in a saucepan over medium-high heat. Simmer for 5 minutes, stirring constantly, until smooth and thickened. Remove from heat and stir in lime juice and soy sauce; season to taste with salt.
Preheat a grill for medium-high heat.
Thread marinated chicken onto skewers, then grill 4 to 5 minutes per side, or until cooked through. Serve with warm peanut sauce.