Trim 12 medium scallions. Halve 10 of the scallions and set aside for charring; finely chop the remaining 2 and place in a medium bowl.
Heat a medium cast iron skillet or grill pan over high heat. Add the halved scallions and sear, flipping occasionally, until charred in spots, 4 to 5 minutes.
Meanwhile, prepare the following, adding each to the bowl of chopped scallions as you complete it: Finely grate the zest of 1 medium lemon until you have 1 teaspoon; juice the lemon until you have 1 tablespoon. Add ½ cup sour cream, ¼ cup whipped cream cheese, ¼ cup mayonnaise, 2 teaspoons rice vinegar, 1 teaspoon kosher salt, and 1 teaspoon onion powder. Stir with a flexible spatula or whisk until combined.
Let the charred scallions cool for a minute, then transfer to a cutting board. Coarsely chop, then add to the dip and stir to combine. Serve with salted potato chips.
