My psu is made by RS and its rated at 1.2A - It was the one recommended at the time (bear in mind it only a pi 1B!)
my file in RETROPIE/configs/all/retroarch-joypads/Xbox 360 Wireless Receiver (XBOX).cfg looks like this http://pastebin.com/fHC1Dm78
my file in RETROPIE/configs/snes/retroarch.cfg looks like this http://pastebin.com/AKqLx0eB
I have also tried inputting all the inputs from the main xbox config file in the snes/retroarch.cfg file without success.
I have since noticed however that the controls work in snes9x2005 (but not 2002?)
cheers