From what I've read, and from what one Sutherland dealer has mentioned to me, he stated that the 20/20 was even more quiet than the older PHD, as well as more dynamic.
One reviewer sort of touched upon the same, saying the 20/20 was more dynamic than the PHD.
The dealer also told me that he really didn't hear a lot of difference with the Linear Power Supply added, so that might be just his own opinion and findings, but it sort of gives some indication that the 20/20 must work quite well with its stock Wall Wart Power Supplies.