For the sauce, in a medium bowl combine sour cream, sweet chili sauce and sriracha; set aside.
In a large bowl combine cornstarch, breadcrumbs, garlic powder, and salt and pepper to taste. Working in batches, add shrimp; toss to coat evenly.
In a deep, heavy-bottomed pot add oil to a depth of 2 inches. Heat over medium-high heat until a deep-fry thermometer registers 365°F. Working in batches, carefully add shrimp to hot oil. Fry 1-2 minutes or until the coating is golden and shrimp are pink. Transfer to a plate lined with paper towels. Repeat with remaining shrimp.
Place cooked shrimp in the sauce; toss to coat well. Sprinkle with scallions, and serve.
