Most effects pedals that run on 9-volt batteries will also run on AC power by using an adapter with a suitable transformer. But just because it appears all AC adapters should be swappable, that's not always the case. In some instances, the end of the cable that plugs into the pedal may appear the same, but won't quite fit into the receptacle, which is lucky for you, since using the wrong adapter could cause damage.

Some people believe that manufacturers tell you to use their brand of adapters and nobody else's simply to assure sales. While there may be some truth to that, the bigger picture is that not all 9-volt adapters are really alike. For instance, you may have a Boss adapter for the PW-10 V-Wah. But if you plug it into, let's say a Fulltone Clyde wah, it may or may not work. Often what will happen is absolutely nothing. That is, you won't get any sound. On rare occasions, you may cause damage to a unit if you're not using the correct adapter - voltages, polarity, and current requirements all vary from pedal to pedal. It's better to have the right adapter on-hand rather than ending up having to replace your favorite effects pedal because you used the wrong one. Or simply stick with powering your pedals with actual 9-volt batteries.

For pedal junkies, there are also several "universal" pedal power units (some pedalboards even have them built-in) that provide a variety of voltages and polarities for powering up pedals from many different manufacturers. These often also include regulated power, and may have circuitry to reduce noise carried by the AC power.

As a final tip, many adapters look alike. Mark each adapter so that you can match it to its corresponding pedal and your life will be much easier!