Before you read further, just a few words. Generally I find it difficult to play around too much with swaps of things. I do it as best as I can, but I tend to go with initial findings for better or worse, so read the following in somewhat of this context, i.e., with a small pinch of salt.
I got the little toy (WR902AC) as well as two Anker battery packs (they slightly differ from the ones recommended in this thread, as Amazon Australia seems to have slightly different Anker models, but they were roughly about the same), so that if one runs out, I can just swap it for the other Anker that’s been fully charged and ready to go.
My system is a Roon server connected to the switch, and another Ethernet cable is connected from the switch to my streamer.
I got the little toy and configured it as recommended in this thread. Powered it with the Anker and removed the streamer Ethernet cable from the switch and plugged it into WR902AC. Yes, it made an improvement compared to the switch I was using, but not to the extent that people seem to be reporting—I think mainly/possibly due to the fact that I have worked reasonably hard to condition my power side of things and also have a grounding device on the switch ground plug.
On an arbitrary scale I would say one notch up in sound quality. I was expecting a little more, but no worries, an increase is an increase, and I have removed the switch in my streaming chain. I would generally say a cleaner and additional detail via the WR902AC.
I did not go back to my previous configuration to double-check things, as I was quite happy with the sound, so I left it as is.
I would say that generally power cables seem to make a bit of difference, so that got me thinking, what would happen if I replaced the USB->Micro power cable that came with the WR902AC. So, I attempted to get a slightly better one. I checked Amazon, I looked at a few, and I chose this UGREEN option, as it seemed to say it was made with copper and seemed to be protected with an aluminum screen. I was particularly interested as it was tinned copper. Not too expensive for 1.5FT. I have put the Amazon US link and not the Amazon Australia link (but it's the same cable).
Amazon.com: UGREEN Micro USB Cable, 1.5FT High Speed Fast Charging USB Cable, Nylon Braided Durable Android Phone Charger Cord, Compatible with Samsung Galaxy S7 S6 Note LG V10 Tablet PS4 MP3 : Electronics
I was playing a well-recorded and well-known-to-me track with the default USB power cable. I paused the track, swapped to the UGREEN from the Anker, and waited for WR902AC to boot up. Once all was done, I resumed play. The improved clarity and cleanness were quite noticeable, so it was well worth the $8 punt. I would say nearly another one notch further up in sound quality. YMMV.
I don’t at this stage plan to buy anything fancier; this was good enough and quite easy to try.
So, thanks everyone for all your contributions to this thread; it's most useful and helpful and resulted in improved sound quality.
Everyone, have a wonderful festive season.
P.S. As my router and WR902AC are in the same room, I don’t have any difficulties playing DXD files (24/364 ?) or DSD256 files even with 2.4Ghz.