Cut each potato in half lengthwise. Place each half flesh-side down on the cutting board and cut each half lengthwise again to make 4 large wedges. Cut each wedge in half lengthwise again for a total of 8 wedges per potato.
Bring a large pot of salted water to a boil. Add potato wedges and boil for about 10 minutes. Drain in a colander.
Whisk olive oil, salt, pepper, onion powder, chili powder, and cumin together in a bowl until smooth. Add wedges and gently toss to coat.
Preheat an outdoor grill for medium-high heat and lightly oil the grate. Grill wedges for 4 minutes. Flip and grill for 4 minutes more.