Inmate E-Stat reports that his Raspberry Pi sounds better with an external USB battery.
The only reason I can think of that might support the improvement from a technical perspective is that the battery is isolated from the AC mains during operation. Otherwise, USB battery packs are essentially DC-DC converters (switching power supplies) in that the relatively low 3.6v from the Li-Ion battery needs to be boosted to 5vdc. If there are 3.6v batteries in series in the battery pack, the higher voltage needs to be bucked down to 5vdc.
As for iFi's marketing department, they really know how spin the tech ;-)
iFi ad from a couple years back:
I think they pulled the ad cuz too many folks laughed at them!
