If using fresh corn, grill or boil the corn until tender, then let it cool and cut the kernels off the cob. If using frozen corn, cook according to package instructions and let it cool.
In a large mixing bowl, combine the mayonnaise, sour cream, lime juice, chili powder, garlic powder, salt, and black pepper. Mix until smooth.
Add the corn kernels, cotija cheese, cilantro, and optional ingredients (red onion and jalapeño) to the bowl. Gently fold everything together until well combined.
Taste and adjust seasoning if necessary. For a little extra kick, add more chili powder or lime juice.
Cover the salad and refrigerate for at least 30 minutes to allow the flavors to meld.
Serve chilled or at room temperature, garnished with extra cilantro or cheese if desired.