As of XY Super Potion's wording allows it be played on a Pokemon with no energy attached, just like Max Potion. You only discard energy if you have healed (up to) 60 damage from one of your Pokemon via playing the card, and if there is no energy to discard you simply do as much of the card's effect you're able to do. This is very different from Super Potion's original wording in Base Set, which required you discard energy first, then heal (it was also only 40 at the time). Under the original wording, you couldn't play it without discarding an energy, but that's not the case with the current version!
Also, you can legally use old Super Potion cards in your deck, but you'll need to keep a current one to the side of your field as a reference since its effect was changed so heavily.
