Power tiles are called as such because of their high point value. Z and Q have the highest point value of 10, followed by X and J with a point value of 8, then K with a point value of 5. As much as possible, save these tiles for premium squares to gain higher points. But be sure to dump them before the game ends or you'll get a higher point deduction instead.

Here is a list of two-letter words in SOWPODS which contains the power tiles. Those that are highlighted are not included in the TWL dictionary.

ZA, ZO, QI, AX, EX, OX, XI, XU, JA, JO, KA, KI, KO, KY