Three years after Michael S. Dell and the investment firm Silver Lake took Dell Inc. private, a Delaware judge has decided that the $24 billion deal was 21 percent too cheap. That said, most investors who held shares in the computer company at the time of the takeover will not be able to collect, owing to the intricacies of Delaware corporate law. In an opinion published on Tuesday, Vice Chancellor J. Travis Laster of the Delaware Court of Chancery found that Dell shares were worth about $17.62 at the time of the 2013 leveraged buyout, rather than the $13.75 that Mr. Dell and Silver Lake paid. The court filing caps a lawsuit brought by a number of Dell investors who argued that they had been shortchanged by Mr. Dell, the founder of the company, which is incorporated in Delaware. Those shareholders brought what is known as an appraisal suit, calling on the Chancery Court to determine the fair value of their holdings at the time.