They tend to be overlooked because of their ubiquitous nature, but the power supply is a very critical and often expensive component that can make or break a piece of audio gear. While their function, officially, is to just supply power, we must remember that this power can and will affect the way the device in question operates. Feed it dirty, unstable power and you'll get commensurate results. "Wall Wart" and "Lump in the Line" type supplies have become popular in recent years because they are inexpensive to build and can be used on a wide variety of devices. These are generally fine for low power equipment (especially if more filtering is employed inside the device), but most high-end pro audio equipment will have an internal supply that is optimized for it.