Here is the full list of all 17 Voltorometer Recharged + achievements.
Beat all the levels in the fifth world
Beat all the levels in the fourth world
Beat all the levels in the third world
Beat all the levels in the second world
Beat all the levels in the first world
Beat all the levels in the sixth world
Beat all the levels in the first special world
Beat all the levels in the second special world
Beat all the levels in the third special world
Collect every orb in every level
Earn a timer medal in every level
Earn a gold timer medal in every level
Beat every level on hard mode
Complete Iron Mode - Not an easy feat!
Complete Iron Mode EX - you're crazy good!
Earn a gold timer medal
Earn a hard mode medal