Uno: With a last card power card, are you allowed to play it after you draw a card?
According to these rules


  If the player has no matches or they choose not to play any of their
  cards even though they might have a match, they must draw a card from
  the Draw pile. If that card can be played, play it. Otherwise, the
  game moves on to the next person in turn.


You need to play the card you just drew. So you can not use the power card.