It would probably be better if they designed it to draw power straight from the power supply. I mean, drawing power from the board sort of defeats the purpose of having a dedicated USB port card. There's only so much that can be done through power filtering. Then again, I've never even heard the noise floor on my USB DAC and I'm not too obsessive so I wouldn't really be interested in a product like this.
Wouldn't it be possible to use a DC-DC converter to drop the 12v supply to 5v with a noticeable improvement in noise rather than filtering the 5v? My PC is noisy, I can hear my mouse and any scroll on a white webpage through a battery powered DAC and amp while using the USB connection (only during quiet parts of a song) so I'm trying to research these cards between Christmas obligations - progress is slow!