Add 2 tablespoons olive oil to a large skillet over medium heat. Add the corn and let cook until the corn starts to char, about 10 minutes, stirring occasionally.
If you are using corn on the cob, grill the cobs until they are nicely charred. Cut the cooked kernels from the cobs.
While the corn cooks, mix the dressing together in a large bowl: mayonnaise, sour cream, Cotija cheese, cilantro, lime juice, red onion, garlic, and chili powder.
When the corn is done cooking, fold it into the dressing.