Combine the mayonnaise, sweet pickle relish, chopped dill pickles, lemon juice, Dijon mustard, chopped capers, onion powder, salt, and pepper in a medium bowl.
Stir all ingredients together until they are fully incorporated and the sauce is smooth.
Taste the sauce and adjust seasoning if needed, adding more lemon juice for tang or salt for flavor.
Cover the bowl and refrigerate for at least 30 minutes before serving to allow the flavors to blend.
Notes
For a sharper flavor, substitute sweet pickle relish with dill relish.
You can make this sauce up to three days ahead; store it covered in the refrigerator.
If you prefer a smoother texture, pulse the ingredients briefly in a food processor instead of chopping by hand.