What's the output? The official one is 9v but .67A http://www.musiciansfriend.com/accessories/dunlop-ecb-003-ac-adapter. If you have too low a current, you will either burn out the supply, trip a breaker or fuse in the supply, or the equipment will not work/fail unpredictably at high load.
If you have too high a current, the system simply won't draw as much power as the supply can provide. The supply might be a little less efficient, but no harm is done.