In a medium bowl, whisk together the diced tomatoes (undrained), beef broth, Worcestershire sauce, smoked paprika, garlic powder, cayenne pepper (if using), salt, and black pepper.
Pour the tomato mixture over the brisket in the slow cooker.
Cover and cook on low for 8-10 hours, or on high for 4-5 hours, until the brisket is fork-tender.
Remove the brisket from the slow cooker and let it rest for 10 minutes before slicing against the grain.
Serve the sliced brisket with the sauce from the slow cooker.
Notes
This brisket is excellent served with mashed potatoes, rice, or crusty bread to soak up the delicious sauce.