Soak the live crabs in tap water for about 30 minutes to purge impurities.Place the crabs in the freezer for 20 to 30 minutes to put them to sleep for easier handling.Bring a large pot of water to a boil and add the ginger slices and black peppercorns.Add the crabs to the boiling water and cook for 5 to 10 minutes until they float.Immediately transfer the cooked crabs into an ice bath to stop the cooking process.Clean the crabs by removing the top shell, cutting them in half, saving the crab fat for the sauce, removing the gills, and cracking the claws slightly.In a large pan, melt the butter over medium heat.Add the finely chopped garlic and cook until fragrant, being careful not to burn it.Stir in the sweet chili sauce, oyster sauce, and chicken powder. Season with salt and pepper to taste. Optionally, add up to ½ cup water to create a thinner sauce.Add the cleaned crab halves and the reserved crab fat into the sauce. Toss for 3 to 5 minutes until well coated and heated through.Serve hot either on its own or over steamed rice.