Space Penguin has ten (10) Energy , but doesn't like any of the available Power Cards. They spend two (2) Energy to discard the three cards for sale and replace them with three new cards from the Power Card deck.
Space Penguin now has eight (8) Energy left. One of the newly revealed cards costs three (3) Energy , and Space Penguin buys it. The bought card is immediately replaced with a new one from the Power Card deck.
Space Penguin may now continue to buy additional cards, or replace the cards on sale, or keep their remaining five (5) Energy and move on to the end of their turn.