Put the spinach, artichoke hearts, onion, garlic, sour cream, mayonnaise, milk, parmesan cheese, feta cheese, red wine vinegar, and black pepper in a slow cooker. Stir ingredients until combined.
Lay the cubes of the cream cheese over the top of the spinach and artichoke mixture. Do not stir in the cream cheese yet.
Cover and cook on low for 2 hours.
Uncover and stir the cream cheese into the spinach and artichoke mixture until thoroughly combined.
Cover and cook on high for 15 more minutes.
Serve with your favorites sides such as tortilla chips, pita chips, vegetables, etc.