In a greased 6-qt. electric pressure cooker, combine cream cheese, sour cream, mustard and garlic powder until smooth. Stir in beer; add bacon, reserving 2 tablespoons. Lock lid; close pressure-release valve. Adjust to pressure-cook on high for 5 minutes. Quick-release pressure. , Select saute setting, and adjust for medium heat. Stir in cheese and heavy cream. Cook and stir until mixture has thickened, 3-4 minutes. Transfer to serving dish. Sprinkle with onion and reserved bacon. Serve with pretzel bun bites.