In a bowl, mix together curry paste, curry powder, salt, white sugar, brown sugar, fish sauce, and coconut milk until you achieve a smooth marinade. Set this aside.
Chop chicken thighs into roughly 1-inch pieces and place them in the marinade, ensuring they are well-coated. Cover and refrigerate for a minimum of 2 hours, or overnight for more flavor.
To make the peanut sauce, combine peanut butter, coconut milk, minced garlic, brown sugar, fish sauce, soy sauce, lime juice, sesame oil, and Sriracha in a bowl. Whisk everything together until smooth, adding water if you prefer a thinner consistency. Adjust the seasoning to your liking, then cover and refrigerate.
Before grilling, soak bamboo skewers in water for at least half an hour to prevent burning.
Once the chicken has marinated, thread the pieces onto the bamboo skewers, making sure they are snug but not tightly packed.
Prepare a charcoal grill, allowing the coals to turn ashy white and become extremely hot. Lightly oil the grill grates.
Grill the chicken skewers over the hot charcoal for about 4 to 5 minutes on each side, or until the chicken is firm and springs back when touched. Ensure the internal temperature reaches at least 165°F (74°C) with an instant-read thermometer.