I have experimented with various usb bus and external supplies. I am using a 1 TB Samsung SSD initially mounted in an " external enclosure". The enclosure provided the option of USB Bus power, Wall wart external supply, and E-sata power from the BDP-2 using the USB only for signal.
http://www.amazon.com/MiniPro-eSATA-6Gbps-External-Enclosure/dp/B003XEZ33Y/ref=sr_1_34?s=electronics&ie=UTF8&qid=1426618414&sr=1-34&keywords=usb+3+ssd+enclosureThe results were intriguing, and clearly confirmed the importance of power supply quality to sound.
First, the external DC power supplies were consistently the worst. I had 2 different wall warts to try, with same specs. Both provided the most closed sound, with the least air and the most "edge" to the extreme highs. Same consistent results whether plugged in to conditioner, wall, same AC circuit or separate. I believe these are cheaply made power supplies, likely spitting out plenty of noise/hash.
Second, USB Bus power from the BDP. Better for sure. Interestingly, there were subtle differences between different usb cables, which was surprising for a non-streaming setup. Probably all about noise.
Third, power from e-sata cable, with signal thru USB. Punchier, much better bass. This was the best external setup, until...
Fourth, internalized SSD powered via sata. That's where I am today. Great all around sound, and no worries about extra power cables and usb cables hanging around and jiggling loose. Sonically and aesthetically the best setup for me.
So...I think Bryston's power is cleaner than external power, and separating power from signal is better than sharing both on a cable.