Preheat the oven to 200 degrees . Line a baking sheet with parchment paper and place in the oven. In a deep fryer or a deep pot fitted with a candy thermometer, heat 3 to 4 inches of oil to 325 degrees . Peel the potatoes and cut into 1/2-inch-thick sticks, placing them in a large bowl of cold water as you work. Soak for 5 minutes, drain and pat dry. Fry the potatoes in 3 or 4 batches until slightly golden at the edges, about 3 minutes per batch (allow the oil to return to 325 degrees between batches). Transfer the partially cooked potatoes to paper towels and let cool while you prepare the fish.
Heat the frying oil to 375 degrees . In a medium bowl, whisk the beer into 1-1/2 cups of the flour until smooth. Season the fish with salt and pepper. Place the remaining 1/2 cup of flour on a plate. Dredge the fish in the flour, shake off any excess flour, then dip in the beer batter. Slowly lower the battered fish into the hot oil and fry, a few pieces at a time, until golden brown, about 4 minutes per batch (allow the oil to return to 375 degrees between batches). Transfer the fried fish to the prepared baking sheet in the oven and keep warm.
Meanwhile, stir together the chili powder, Old Bay Seasoning and 1 teaspoon of salt. With the oil at 375 degrees , fry the potatoes a second time, in 3 or 4 batches, until crisp and golden brown, about 4 minutes per batch. Remove the chips to fresh paper towels to drain and immediately season with the spice mixture. Serve the chips with the fish and malt vinegar.