In a medium bowl, stir together using a mixer or by hand, cream cheese and sour cream. Fold in the crab, water chestnuts (if using), 1/4 cup green onion, the powdered sugar, soy sauce, and garlic powder.

Cover and chill for 2 to 24 hours.

To serve the dip warm, heat it in the microwave for 1 to 2 minutes on 100% power [high], stirring every 30 seconds or heat in an ovenproof casserole at 350 degrees, or until warm throughout.

To serve, drizzle the cold or warm dip with sweet and sour sauce or Thai Chili sauce (optional) and garnish with additional sliced green onion. Serve with wonton chips.