Preheat an outdoor pellet smoker to 225 degrees Fahrenheit (107 degrees Celsius).
Rub 1 (2 pound) beef tri-tip roast with 1 tablespoon olive oil on all sides to coat.
In a small bowl, stir together 1 1/2 teaspoons salt, 1 teaspoon black pepper, and 1 teaspoon garlic powder. Season the tri-tip evenly with the spice mixture, coating all sides.
Place the tri-tip on the smoker rack. Close the lid and cook until the internal temperature reaches 125 degrees Fahrenheit (52 degrees Celsius), about 90 minutes. Cooking time may vary depending on the thickness of the roast. Use a meat thermometer or probe for accuracy.
Transfer the tri-tip to a large baking sheet and loosely wrap with aluminum foil. Let rest while increasing smoker temperature to 450 degrees Fahrenheit (232 degrees Celsius).
Melt 1/4 cup salted butter. Return the tri-tip to the smoker and baste with the melted butter. Sear both sides of the tri-tip until the internal temperature reaches 145 degrees Fahrenheit (63 degrees Celsius) or desired doneness, about 5 to 10 minutes total.
Remove from the smoker. Let rest for 5 to 10 minutes before slicing. Slice against the grain to serve.