@chungjh iFi has product that fits between a power supply and component: DC iPurifier2. Site says that it supports "5-24v DC (up to 3.5A, 84W)." I might try it for myself. It's already pretty affordable by HiFi standards, but if you don't like the results when using it with your router, you can always place it on another component where it has a greater benefit. I'm considering trying it for myself. iFi even advertises using it with a low noise power supply. Might be worth a shot