DIY PT's are mostly 5v ... which you probably want for the Dual Coils (DCs) anyway. You need enough amps to power two 3.2 ohm coils at the same time (hence 1.6 ohm DC). That's over 3 amps. Make sure your wall wart/ac adapter/usb charger port device can handle that. Also you want a REAL HEFTY button on the PT, or a real hefty mosfet. See the modders section now (although you can post there yet, you can read it). You'll want the heaviest USB cord too, so it doesn't have too much resistance, or make your own with proper connectors.
It's basically an [Atty Center Connector] -> [Button] ->[Positive Wire]-----cord-------[USB Connector]-->[power supply] with the other wire being a ground connection to the outer shell of the atty connector. The data wires are normally not used.
You might want some strain relief on the cord and an optional LED/resistor for an indicator.
I'd go at least 4 amps on the button, or use a mosfet at least 4 amps (higher is better like 6 in this case) since your pulling a theoretical 3.125 amps.