The Athletics also recalled right-hander Michael Brady from Nashville while optioning outfielders Jaycob Brugman and Mark Canha to the same club.
Powell was acquired on Sunday in the deal that sent All-Star first baseman Yonder Alonso to the Seattle Mariners. The 24-year-old had a major league stint with the Mariners earlier this season but batted just .194 in 23 games.
Powell hit .340 in 58 games at Triple-A Tacoma prior to the trade. The left-handed hitter was 4-for-16 in three games for Nashville.
Brady is beginning his third stint of the season with the Athletics. He posted a 4.15 ERA in eight appearances.
At Nashville, Brady is 3-1 with a 3.21 ERA in 17 appearances (eight starts).
Canha struggled in 34 games this season for the Athletics, batting just .210 with four homers and 10 RBIs. He is hitting .271 with 12 homers and 46 RBIs in 66 games with the Sounds.
Brugman batted .266 with three homers and 12 RBIs in 48 games with Oakland. He is hitting .288 with one homer and eight RBIs with Nashville.