take any 5v power rail, hook the ground up to ground on a USB mini connector, and the 5V to the 5V pin and the teensy will power up when you plug in the mini USB. the teensy only asks for 500ma, so as long as your power supply can give it that, you're good. in the US, the cheapest reliable USB wall warts are probably monoprice's. otherwise, i'd say buy like 5 off of ebay from an HK seller with high feedback, test them all and just toss the ones that don't work.