Thinly slice the onions.
Add the onions, butter, brown sugar, beer and salt to a slow cooker. Cook on low for 8 to 10 hours or until soft and dark. Stir occasionally, if possible.
Add the cream cheese, sour cream, Worcestershire, and garlic powder.
Cook on low for two hours, stirring occasionally. Stir in the pepper, salt to taste.
Add to a serving dish, sprinkle with green onions.