DuPont is a pretty well-run company. Under the leadership of Ellen Kullman, a company veteran who became its chief executive in 2009, this once unwieldy conglomerate has undergone a great deal of change, with more still to come. It has cut some $2 billion in costs, eliminating a third of its management; announced the spinoff of its performance chemicals business; and “refreshed” its board with such corporate stalwarts as Edward Breen, who is best known for turning around Tyco International in the early 2000s. Since Kullman took over, the company has delivered 266 percent in total shareholder returns, easily outpacing the Standard & Poor’s 500-stock index. It is in the middle of a major restructuring designed to boost earnings growth.