PepsiCo—which faced a consumer backlash after it pulled aspartame from Diet Pepsi in 2015—is making a full reversal and will once again use the controversial sweetner in the soda's mainstream variety. The brand yanked aspartame in mid-2015, replacing it with with sucralose and acesulfame potassium, known as Ace-K. But the move backfired as loyalists clamored for the original formula. So in 2016, the brand brought back the aspartame version—but only in limited quantities marketed as "classic sweetener blend." It kept the aspartame-free version as its mainstream variety. But now Diet Pepsi is making the aspartame version its main variety again...