I used iFi power supplies. They have two different models to match most various voltage and amperage requirements for streamers, DACs, modems and routers. iFi is relatively affordable, which makes it a perfect to start to see if you hear a difference compared to your streamer's wifi card. If you do try a low noise power supply with your modem and router, I'd be interested whether the difference was obvious (or worth the cost) in your system.
Just as a side note, I suspect that a reclocker and power supply / power cable upgrade should be prioritized over power supplies for the modem and router. iFi also makes a few reclockers in case you haven't tried one. I suspect that a Node 2i, for example, would benefit from a reclocker; but I also suspect that most Node owners don't run a reclocker.

