Electrode-EX's "Crush and Burn" attack does extra damage based on the number of Energy cards discarded, not the amount of Energy provided. Official Wording: You may discard as many Energy cards as you like attached to your Pokémon in play. If you do, this attack does 30 damage plus 20 more damage for each Energy card you discarded.
Source: PUI Announcement (2004-12-16)