I'll chime in here, as I am likely one of the only ones around here that use linear supplies on my router and NAS.
Short answer, I would not be without them after hearing the difference on these 2 items.
Further: Dynamics became startling vs the stock supplies that came with them. Everything improved, bass slam, image focus, depth, height, tone, vividness, delineation, contrasts from soft to loud, 3D, etc... Night and day difference, and I believe it has to do with speed and power delivery vs. the stock supplies.
However, I am using all Paul Hynes linear supplies. These are great linear supplies and there really is nothing else like them for digital stuff. Trying some of the other offerings out there, and you will likely be better off with just the stock supplies. That's the reality of it. Just because it is linear vs a switch mode supply doesn't mean it will be better. It has to be a good supply, nonetheless.
I need to talk Dave at PI Audio into letting me try his battery solutions as I hear wonderful things about them. There are likely other great battery solutions as well, but I have no experience using any of them.
Filter USB? The Totaldac USB Cable/Filter does an exceptional job of that, and is the USB Cable to beat IMO.