"Powerup" means that you for a limited amount of time will be equipped with an extra quality. There is no standard translation of the word to Norwegian. If the "powerup" gives you extra strength, you can translate it by "ekstra styrke", if it give you speed, you can use "ekstra fart" or "turbo".

If you want to use the word in a generic sense, I recommend to leave it untranslated, as "powerup" will be understood by must gamers.