Preheat oven to 350 degrees.
Cook penne pasta 2 minutes less than package directions. Strain & rinse pasta in cold water & set aside.
Melt butter in large saucepan over medium heat and whisk in the flour. Continue whisking and cook for 2 minutes.
Slowly add milk, whisking constantly. Cook until the sauce thickens, about 10 minutes. Stir frequently. Remove from the heat.
Add the cheese, salt, chili powder, and garlic powder. Stir until cheese is melted & ingredients are thorougly mixed, about 3 minutes.
Combine the cooked pasta and sauce in a medium bowl or pot and mix carefully, but no thoroughly.
Pour the pasta into a 9x13 baking dish. Sprinkle the remaining cheese and chili powder evenly on top.
Bake uncovered for 30 minutes. Allow the mac & cheese to cool for 5 minutes before serving.