Preheat oven to 425°F (220°C). Cut potatoes into 3/4-inch wedges, toss with olive oil, garlic powder, onion powder, smoked paprika, salt, and black pepper. Spread in a single layer on a baking sheet and roast for 25 to 30 minutes, flipping once at 15 minutes, until edges are golden and crisp.

While fries roast, cook bacon strips in a cold skillet over medium heat for 8 to 10 minutes, turning once, until crispy. Transfer to a paper-towel-lined plate, cool for 2 minutes, then crumble.

In a small saucepan over medium-low heat, melt butter. Whisk in flour and stir for 1 minute until pale gold. Gradually whisk in whole milk and stir for 3 to 4 minutes until the sauce coats the back of a spoon. Reduce to low, add cheddar and cayenne, and stir until smooth. Remove from heat and stir in sour cream.

Transfer hot fries to a serving platter, pour cheese sauce over the top, scatter crumbled bacon, and finish with sliced green onions. Serve immediately.