Powell attended Junípero Serra High School, where he was a two-way player at wide receiver and cornerback.
As a sophomore, he helped preserve a 46–38 triple-overtime win against UCLA, by making an interception in the end zone.
As a junior, he was limited with hamstring and groin injuries that forced him to miss all of spring practice and 4 regular-season games.
As a senior, he registered 42 tackles, 5 interceptions (tied for the conference lead), 13 pass deflections and 32 punt returns for 389 yards (12.2-yard avg.).
Powell was signed as an undrafted free agent by the Detroit Lions after the 2003 NFL draft on April 29.