[0.02c hitting the floor]
My experience with USB-powered audio interfaces - specifically the MBox2 - is that yes, the preamp can handle powering the condenser mics but the signal quality is compromised by electrical noise added during the transfer via the same USB cable carrying power to the unit.
(this is also true for recording line-level signals such as keyboards which do not need phantom power)
The 3rd gen MBox series may have resolved this problem. I know there are HRs out there who record with other USB-powered devices and don't seem to have the same low level high frequency noise problems as the MBox does.
[edit: I should clarify that the electrical noise is low in level and would most likely be hidden when buried under other instruments, but if you have a solo instrument song or several tracks recorded using the same device all adding small amounts of the same electrical noise, it really does become noticeable.]
Last edited by Dags; 02-12-2013 at 19:57.
I don't suffer from insanity; I enjoy every minute of it.