I like to use 7.5V walwarts you can get cheap on Amazon or EBAY. For any of the Arduino stuff with linear regulators, they keep the power dissipation low. I also paint the tips of my walwarts. Blue=5.0V, gold=7.5V, yel=9.0V, red=12.0V many things don't like the wrong voltages. If my daughters only knew where there nail polish is going.