Prepare pork belly: Remove skin if attached. Trim excessive fat to ¼ inch. Cut into 1½-inch cubes. Season with salt, pepper, garlic powder, and onion powder. Let rest 15-20 minutes at room temperature.
Preheat smoker: Set pellet smoker to 250°F. Fill hopper with cherry or apple wood pellets. Preheat 10-15 minutes. Position drip pan below grates.
Smoke pork belly: Place cubes directly on grill grates with space between each. Close lid, smoke 2 to 2½ hours until internal temp reaches 165-175°F and deep mahogany bark forms. Don't open lid during smoking.
Make glaze: In saucepan over medium heat, combine raspberry jam, ketchup, Worcestershire sauce, vinegar, honey, garlic powder, onion powder, and red pepper flakes. Simmer 5-7 minutes, stirring frequently. Taste and adjust seasonings. Remove from heat.
Glaze and caramelize: Transfer smoked cubes to foil pan. Pour glaze over and toss to coat completely. Increase smoker to 275°F. Return pan to smoker uncovered. Cook 45-60 minutes until sauce caramelizes and internal temp reaches 195-200°F.
Rest and serve: Remove from smoker. Rest 10-15 minutes. Optional: brush with fresh glaze for shine. Serve warm with toothpicks.