Now for debug/test I use this power conversion board (1$!!) with a 12V wall adapter, out 3.3v or 5v, 700mA max :
http://www.ebay.com/itm/171907055454
In the final project I usually use this power converter, also 1$, input 4.5-28V, max 3A out with adjustable output voltage:
http://www.ebay.com/itm/381374427427