Lightly grease the insert of a 6-quart slow cooker with non-stick cooking spray.
In a medium mixing bowl, whisk together the chicken broth, softened cream cheese, garlic powder, onion powder, and black pepper until mostly smooth.
Layer the frozen pierogies and the sliced kielbasa into the prepared slow cooker.
Pour the broth and cream cheese mixture evenly over the pierogies and kielbasa.
Cover and cook on low heat for 3 to 4 hours, or until pierogies are tender and the sauce has thickened.
Spread the shredded cheddar cheese over the top of the casserole.
Cover and cook for an additional 10 to 15 minutes, or until the cheese is fully melted and bubbly.
Garnish with chopped chives or green onions before serving.