Bill,
Good point regarding the "dirty" DC that usually comes out of a transformer. There is usually a high amount of ripple coming out of them. They are used quite often as a supplement to, or to charge the batteries in a device. When used as a "battery eliminator", the device will have a filter circuit to clean up the ripple. In the case of rechargeable batteries, the batteries themselves will filter out quite a bit of ripple. To make a long story short, if a device is designed to use batteries only, use batteries only. If it was designed with a external DC source as an option, there would have been a jack to plug it in to.
Jeff
