There is no official representative from Pro-Ject here. The lead developer,
@JohnW who is not a Pro-Ject employee, has been posting here on his own time.
To summarize previous posts:
• The manual says we should use the included switching PSU for coaxial and optical input only, and when connected via USB we should not use the PSU.
• A few months ago
@JohnW encouraged us to ignore that part of the manual and experiment with using external adapters with USB for better sound quality. When an external power adapter is connected, the device auto-switches from USB power to the adapter. All or most of us have found this improves the sound.
• At the end of December, John stated that we should do this only with a linear or battery PSU. See his posts at the top of this page and the end of the previous page for further explanation.