Add the ground beef to a large skillet and place it over medium heat. Cook, breaking the meat up as it cooks, until browned through, about 8 minutes.
Season the beef with salt, pepper, and garlic powder and stir to combine. Drain any excess grease from the pan. Remove from the heat.
Pour one jar of pasta sauce into the bottom of the slow cooker. Break the spaghetti noodles in half and place the noodles over the sauce. Pour cooked beef over the noodles. Then sprinkle with Parmesan cheese and top with cubes of cream cheese. Pour another jar of pasta sauce over the cheeses.
Cover the slow cooker and cook on HIGH for 3 hours.
After 3 hours, give the pasta a good stir (it will be thick). Add the last jar of pasta sauce and 1 cup of chicken broth, and then stir to combine. (You can add up to 2 cups of chicken broth total, depending on how thick you like your sauce.)
Cover the slow cooker again and cook for 1 more hour. Stir and serve warm topped with more Parmesan and chopped parsley for garnish, if desired.
Notes
You can turn the slow cooker to WARM if you're not ready to eat right when the pasta is done cooking.
Since slow cooker heat varies slightly by model, the spaghetti may take extra time to cook. Start checking if it's al dente about 45 minutes after adding the last jar of sauce and chicken broth. If the pasta needs more time, check every 15 minutes until it's cooked to your liking.