Whisk onion powder and wine together and pour in the slow cooker.
Sprinkle garlic and taco seasoning on steak and then place in the slow cooker.
Cook on low 8 hours.
Remove meat; cool slightly then shred with forks or with a paddle attachment in a mixer.
Spoon beef on tortillas, adding leftover juice from the crock to moisten if desired. Top with traditional items such as lettuce, tomatoes, cheese and sour cream.
Recipe by Three Different Directions at https://www.threedifferentdirections.com/slow-cooker-beef-steak-tacos.html