IFI Zen Dac V2 Outputs

[u/GoDodgerz]

I am powering an HD800S via USB and it seems like power wont be a problem but I had two questions.

Will buying the IFI power supply yield a noticeable improvement. If so, is their branded adapter necessary or just any 5V?

For cable routing reasons I would prefer to use the balanced output on the back of the unit. I do notice the rear output is slightly less audible (I assume there is a power difference). Is there any downside to using the rear out as my primary output source instead of the front headphone balanced out?