Is it ok to give external dc power to a usb device which needs 9volt 150mA - 180 mA with 9 volt and 500mA.?

I hav a usb device which requires dc power supply of 9volt @ 150mA - 180mA max. Using buspower does not give smooth running. The only adapters available have current @ 500mA to 1.2mA or more. Is it ok to use adapters with more amperage? Or will it affect the device adversely. What will hapen if i use an adapter with higher amperage. Since the manufacturer has specified the 150 - 180mA as maximum, I'm in a situation. Plz help.