Newcastle's youngsters, who kicked off their Northern Section Group C campaign with a 3-1 comeback win at York City last week, took the lead on the stroke of half-time at Mbanq Valley Parade courtesy of Matheos Ferreira's curling strike from 20 yards.
Bradford, occupying top spot in League One, drew level towards the hour mark courtesy of Powell's close-range header before the Bantams substitute's fierce drive in the closing stages proved the difference, with the visitors reduced to ten men in stoppage-time following Johnny Emerson's straight red card.
Under-21s Lead Coach Robbie Stockdale made three changes from Saturday's Premier League 2 clash away at Leeds United.
Miodrag Pivaš and Mason Miley, both named on the bench for the Magpies' Premier League win against Hull City last weekend, were named in the starting XI while 16-year-old goalkeeper George Mair replaced Roman Dowell, the latter receiving a first call-up for England at Under-18 level, in-between the sticks,
Bradford created the opening shot in front of goal as Corey O'Keeffe capitalised on Logan Watts' pass but sent his effort from the edge of the box wide of the target.
Newcastle, who defeated Bradford via penalties in the group stages of the 2023/24 tournament following a 2-2 draw, went in search of an opener as Alfie Seldon's teasing free-kick almost landed into the path of Afner Cá but the Guinea-Bissau striker, who scored his first goal for the Magpies during last week's victory at York, was unable to make contact with the ball inside the penalty area.
In front of 2,132 spectators, including 51 travelling away fans, the hosts struck the woodwork shortly after through O'Keeffe as the Bantams full-back's fierce free-kick on the edge of the box crashed onto the crossbar.
Macaulay Gillesphey, who spent seven years at Newcastle's youth set-up, went close to scoring against his former club as the Ashington-born defender latched onto Henry Cartwright's low free-kick from the right wing but steered a first-time effort over the bar.
Ferreira, who made his senior debut for the Magpies during July's pre-season friendly against Gateshead, was unfortunate not to fire the visitors into an earlier lead as the 18-year-old winger collected Seldon's pass on the edge of the box before his powerful drive at goal was pushed out for a corner by Bradford goalkeeper Cameron Dawson.
In the 42nd minute, however, Ferreira got his name on the scoresheet in stunning fashion. After Cá raced onto the teenage forward's initial forward pass, the African frontman returned the favour before Ferreira curled a delightful shot from the edge of the penalty area into the top-right hand corner.
Cá almost turned from provider to goalscorer in the final stages of the first half as the physical striker, who joined Newcastle's Academy last summer following the expiration of his contract with La Liga side Levante, cleverly evaded his marker on the right byline but saw his resulting effort from a tight angle blocked out for a corner.
Newcastle found themselves on level terms in the 59th minute as Powell, introduced from the bench two minutes prior, rose from Bobby Pointon's dangerous cross from the left wing before the substitute's header squirmed into the net.
Dylan Charlton, who made his first senior start during Newcastle's pre-season friendly against Strasbourg at St. James' Park in August, was unable to restore the visitors' advantage as the Gateshead-born left-back controlled Cá's inviting pass inside the box before lashing his attempt wide of the left-hand post.
Newcastle's second-string fell behind in the 72nd minute as Powell doubled his and Bradford's tally. After O'Keeffe managed to keep the ball in play on the left byline, his resulting cross found Powell at the back post, who chested the ball before smashing a low effort into the bottom left-hand corner.
United's hopes of a late leveller took a difficult blow as Emerson was sent off in the closing minutes of the contest following an altercation towards the corner flag.
Newcastle United Under-21s: George Mair, Scott Bailey (c), Dylan Charlton, Luke Craggs (Kacey Wooster 85), Miodrag Pivaš, Logan Watts, Afner Cá, Henry Johnson, Matheos Ferreira (Jayden Kouossu 72), Mason Miley (Kyle Fitzgerald 73), Alfie Seldon (Johnny Emerson 66).
Subs not used: Tyler Jones, Fraser Harper, Isaac Moran.
