I don't believe anyone has answered your question. Then again, it has been covered many times. The power supply is the heart of any audio component. In recent years, switching wall-wart power supplies have become popular because they work very well and cost the manufacturer a tiny fraction of a robust linear power supply. The power supply in theory isolates everything that comes after it in the circuit from RFI, EMI, DC, and dirty power "hash". It also, when well-designed and implemented, provides for dynamics, authoritativeness, propulsion, etc.
The more expensive a component is, the more likely it is that it will have a robust power supply. Switching PS's are a cost cutting measure, virtually always. Generally speaking, an outboard PS that connects with a thin wire and 6mm pin is not going to be optimum. An outboard PS has great advantages in terms of avoiding transformer induced noise spuriae, usually at 60 hz in the US, but only if connected with a beefy and well designed umbilical connection. The Manley Steelhead phono stage is a good example.
For better or worse, there is once again a lot of intellectually honest debate on this subject. One camp insists that if any component, including a DA, is a featherweight, it is bound to be lacking in the above qualities. Again to be clear, this applies to pre-amps, amps, phono stages and DAC's. When it comes to very high end DAC's, it is rare to find the lightweights but they are out there. Chord is one example. Benchmark is another.
