Begin by soaking the cut fries in cold water for at least 30 minutes to remove excess starch. This helps achieve a crispier texture when frying.
Heat the vegetable oil in a deep fryer or a large heavy pot over medium-high heat until it reaches 350°F.
Drain the fries and pat them dry with paper towels. Fry the potatoes in batches for about 5-7 minutes, or until golden brown and crispy. Remove and drain on paper towels.
In a large bowl, combine garlic powder, onion powder, smoked paprika, cayenne pepper, salt, and black pepper. Toss the hot fries in the spice mixture until evenly coated.
Arrange the seasoned fries on a serving platter. Drizzle with ranch dressing, then sprinkle with cheddar cheese and feta cheese, if using. Top with chopped green onions.
Serve immediately while hot and crispy.