If you are connecting the power supply to the Pi with anything besides the cable that came with the power supply, you could be loosing voltage on the additional wire.
I have found several of the cheap micro usb extension cables to be very poor quality.
The wires inside the cable are very small and will produce a voltage drop, which the pi dont like.
Also, if you have a arcade cabinet power supply laying around you can use it to power the Pi. Just put a volt meter on it first and make sure it is set to put out 5 volts. Most of those power supplies have a pot you can adjust to get approx 4.5 to approx 6.5 volts out on the 5 volt terminals. Pi dont like high voltage either. 5-5.2 is probably about right.