|The 7.7A is the maximum that the adapter can supply. If the device only needs 3.34A, that's all that it will draw. Any device only draws the amount of current it needs (assuming that it's not defective).|
But if it's DC, the adapter's polarity does have to match the device.
FWIW to XP users: When you click on the 'Command Prompt' you are just causing the 'Command prompt' to be displayed. This prompt gives you access to NTVDM.EXE, the 'NT Virtual DOS Manager'.