I want to comment that the build quality on the U18 is first rate. It is definitly on par with Yulong's other top line products such as the A18 and D18 and is quite at home sitting next to those units.
I can comfortably say that the sound quality is slightly better through the U18 when using the external power supply. Not a "night and day" improvement but a noticeably quieter background is apparent. I suspect many USB converters would benefit being removed from the noisy power environment of a computer but not all offer the option.
Though not a specific benefit of the U18 alone, I also appreciate having access to native 88.2khz and 192khz bitrates and not having to resample them.
Edited by mrcasey - 10/19/12 at 12:24pm