Place the rinsed baby carrots into the insert of a 4-quart or larger slow cooker.
Add the water, butter cubes, white sugar, 2 tablespoons of brown sugar, garlic powder, and salt over the carrots.
Stir gently to distribute the seasonings and sugars evenly throughout the carrots.
Cover and cook on LOW for 6 hours or on HIGH for 3 hours. The carrots should be fork-tender but not falling apart.
Drain the excess liquid from the slow cooker pot carefully.
Transfer to a serving dish and sprinkle lightly with a little extra brown sugar for a glossy finish before serving warm.