[NAME]-G  Based on your display plans and the fact that you're using an XPS 15 model, the WD19TB and WD19TBS are your best choices, for the simple reason that they are the only docks that will provide the 130W amount of power that your system is designed to have for optimal performance.  The official USB PD spec that existed when those products created maxed out at 100W, but Dell did something proprietary on some of their systems, including yours, and some of their docks, including the WD19TB and WD19TBS, to support running 130W over USB-C/TB3.  But you won't find that implemented on third party products, or even all Dell docks.  So if you use another option, you'll either have to put up with slower battery charging and reduced performance as your XPS attempts to adapt to an undersized power source, or else keep the XPS power adapter connected to your system as well, which of course anchors it there rather than freeing that power adapter up to be parked elsewhere or just sparing you having to unpack and repack it as you come and go, as would be the case if the dock itself was an adequate power source.As for reviews, those aren't everything, especially with products like docks that tend to generate negative reviews by people who didn't know how to set them up properly and/or didn't realize that the dock wasn't designed to do something they expected, at least with their system.  You might be amazed how many people I help here who post topics because they're frustrated their dock isn't working as expected, and I either have to explain what they have to do to make it work as they want or why their setup will never work the way they wanted.  Both situations often could have been avoided by the customer doing more research beforehand or reading the dock's manual, but not everyone does those things.  And of course some people don't bother to post topics here and instead just return a product and write a bad review.In terms of your future display plans, if your main focus is productivity, I would very strongly suggest that you consider 27" 1440p displays rather than 4K.  A 27" 4K display results in a pixel density of 163 ppi, which is high enough that you have to enable Windows display scaling -- which many applications still don't handle optimally -- but NOT high enough to give you that razor sharp "Retina display" experience.  You'd need 5K resolution for that on a 27" display, but your system doesn't support 5K displays, nor would a Thunderbolt dock be able to run two of them due to the bandwidth requirements of that setup.  A 27" 1440p display meanwhile has a pixel density of 108 ppi, which is pretty standard, so it would be usable by most people at the standard 100% scaling setting.  (For reference, your current 21.5" 1080p displays have a pixel density of 102 ppi.)But if you do go dual 4K, be aware that with the WD19TB and WD19TBS, there are only certain display output combinations that will work with dual 4K, and they vary based on the capabilities of the source system.  The reason for this has to do with how the dock allocates video bandwidth received from the system across its outputs.  Your system is a DisplayPort 1.2/HBR2 over Thunderbolt system, so with your system, one 4K display would need to be connected to the downstream TB3 port at the edge of the dock, using a USB-C to DisplayPort cable if your future display didn't have a native USB-C input.  The other could use any other output.  If you don't use that port setup, your 4K displays will run at 30 Hz rather than the normal 60 Hz.  (This is a perfect example of a situation that can generate negative reviews that aren't entirely fair since user lack of awareness is at least partly responsible for this.)Regarding the TB vs. TBS model, the only difference is that the latter lacks a headset jack, and the reason is that the global supply chain shortage somehow prevented Dell from sourcing the materials required to incorporate that jack and the audio chipset to run it.  So instead of stopping all dock production, they created new "S" models that lacked that feature to keep production running.  There are USB headset/headphone audio adapters if you really need that jack.In terms of the system, I'm not overly concerned with you using an older XPS 15 model for work purposes from a performance standpoint, but if this will be a business-critical system in that your wife would not be able to resume working on some other system if it unexpectedly developed a hardware problem, I tend to advise my own IT clients to consider making sure their business systems are always covered by not only a warranty, but one with next business day on-site service.  The standard warranty entails mailing your system to Dell and potentially waiting weeks to get it back.  On-site means someone comes to you and fixes it then and there.  But your 9550 wouldn't have any warranty coverage at all.  I would look at either your wife's salary or her hourly billing rate, depending on the nature of her accounting business, and consider whether risking even a few days of downtime is worth declining to purchase a new system that would have solid warranty coverage.
My wife has a XPS 15 9550 laptop with the following specs: BIOS: 1.5.1CPU: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHMemory: 16GBGPU: Intel(R) HD Graphics 530 & NVIDIA GeForce GTX 960MIntegrated Monitor: 4K (3840x2160) with touch support. External Monitors (X2): HP EliteDisplay E222  1920x1080 60Hz. They have VGA, HDMI & DP1.2 ports (she uses them working from home in her current "day job" with her employer provided laptop. They will go away when she transitions to working for herself at a point in the near future) She is an accountant and we are looking at replacing her monitors with 27"  4K monitors at some point in the future. She would like to connect the 2 current HP monitors to her XPS and also have the XPS screen visible. They have a spare DP port on each monitor not currently being used. So, my question of the best solution is keeping in mind both current and future monitors, providing an ethernet connection (when she move to working for herself I plan to run LAN from the router to her XPS which has no ethernet port). It is not critical that the solution have power but she would like a few additional USB 3.0 type A ports. And she will be using the XPS screen in addition to two external monitors. The XPS is running Win10. Here are some solutions I've found. Would like advice on the best option given her wish list. $360 Dell WD19TB (Amazon) - expensive but has all connectivity (addtl USB ports, ethernet...) Not available thru Dell. Gets mediocre reviews $303 Dell WD19TBS (Dell) - cheaper then above but no headphones or audio chip the WD19TB has' Also gets mediocre reviews $158 (Makertech) Startech DK30C2DAGPD - even less expensive, has ethernet, USB ports, and can run two 4K monitors though over HDMI (I've read on here that DP is the better option) $100 (Amazon) Plugable ‎USBC-6950-DP dual 4K over DP plus ethernet. No addtl USB ports $80 (Amazon) Cable Matters 107015-BLK - has duel 4K over DP, ethernet and one USB-3 port. Looks good for the price considering power in not a must have. ~$47 total (Amazon) - buy a HDMI to DP cable and a TB3/USB-C to DP cable for ~$23. Also buy a USB-C to Ethernet adaptor for ~24 which also has 3 USB-3 ports. Have 3 cables to plug or unplug for this cheapest option. Any other options and/or opinions a GREATLY appreciated. Don't want to be penny wise and pound foolish.   
XPS 15 (9550) Futureproof Dual Monitor Setup?