Cut the potatoes lengthwise into ¼ inch thick slices, then cut each slice into ¼ inch thick fries.
In a medium bowl, toss the potatoes with the oil. Season with the salt, garlic powder, and pepper to taste, tossing to coat.
Preheat the air fryer to 380℉.
Working in batches, arrange a single layer (no overlapping) of the potatoes in the air fryer basket. Cook for 12 to 15 minutes, flipping halfway, until the potatoes are golden and crisp. (For a toaster oven-style air fryer, cook at 350 degree F; the timing remains the same). Serve immediately.