Your power supply problems just got SOLVED! This little circuit board may look tiny but inside is a high efficiency DC/DC step-down converter which can output up to 3 Amp at 5V without the need of any heat-sink or forced cooling. (It does get a bit toasty at 3A though) UBEC stands for "universal battery eliminator circuit" and this UBEC is designed to replace a 5V supply in RC planes and 'copters but its also great for any kind of microcontroller or electronics project that runs off of 5V. Adafruit tried a half dozen different 'BECs and found this one to be the best in terms of range and stability. You can check the technical tab for the analysis of input/output range and current draw.

To use, connect 6V up to 16V (recommended) to the IN-side wires and 5V will be generated on the OUT-side wires. You'll get 5V (+-5%) regulated output from higher voltage input. 3A output current, 5A peak - if you're trying to draw 3A you'll need to give it a little more than 6V though, 7V works well. The UBEC has built in filter capacitors on the input and output, but its a switching supply so its a little noisy compared to a linear regulator.

Adafruit pulled the heatshrink off of one and found an MP2307 you can check the datasheet for conversion efficiency and other specifications.

UBEC DC/DC Step-Down (Buck) Converter - 5V @ 3A output (0:40)