Conversion Apparatus is a rare Artifact card from Modern Horizons 3 Commander (M3C), collector number 128. Current market price: $0.28, TCGplayer market prices via Scryfall.
{T}: Add {C}. {3}, {T}: You get {E}{E}{E} (three energy counters). {T}, Pay {E}{E}{E}: Add three mana in any combination of colors.