Cook and stir beef, onion, and bell pepper in a large pot over medium heat until beef is browned and onion and pepper are tender, about 10 minutes. Drain and discard grease.
Stir in beans, tomatoes, tomato sauce, chili powder, jalapeños, red pepper flakes, black pepper, salt, and garlic powder. Bring to a slow boil, then cover and reduce the heat. Simmer chili, stirring occasionally so it does not stick, for at least 30 minutes or up to several hours; the longer it simmers, the more flavorful it will be.