Guys, please note that different Amper ratings is not the key factor here. It should be just enough to feed the device. As I mentioned above, something between 1 and 2 Amper should be quite enough. If one pays more for more powerful adapter, he just wastes his money.
But voltage (i.e. electrical potential ) is the key factor. If one prefer rather subtle vibration than strong, that may be a way to go. I would recommend to play around with values from 7 to 9 Volts. I could see in stores adapters featuring the variable output, which could be handy for fine tuning.