Most people’s idea to improve the power of a USB device is to replace the USB power with an external linear supply. Although this kind of mod would improve the incoming power to the device, the ultimate noise performance is determined by the local regulators that directly feed the chips.
Additionally, because I value the convenience of using USB power, I took a different route: I decided to replace the local regulators with low noise types. The factory regulators are AMS1117. The ones I am upgrading are LT1963. Noise density figures for the AMS1117 is approx 990 nV (3.3v regulator) and for the LT1963 is approx. 125 nV (3.3v regulator).
The AMS 1117 regulators are similar in noise performance as the very popular LM317 types. The LT 1963 are cousins of the LT 1763 used in Buffalo II. They have higher noise (but are still low noise) due to their higher current carrying capability.