@dainova  Because the E-Port dock and E Series systems were introduced in 2008. Back then the underside dock connector on the laptops was closer to the center, which meant that when you docked the system, the back half of the laptop occupied that space where you have a gap. (The slider on the dock unit that can extend or retract part of the main dock unit exists to account the fact that some laptops had optional high capacity batteries that would protrude out from the rear edge of the chassis.) With the Exx40 models introduced around 2015 (I think) and models after that, the underside connector got moved to the rear edge of the system — not sure why — and that goofy spacer was introduced. I guess Dell chose to maintain compatibility with what was by then a huge installed base of E-Port docking stations in businesses rather than introduce a brand new dock model that would make it harder for businesses to support multiple employee setups, especially in “hot desk” environments where you never know which person and therefore which laptop will be used at the desk. Another possible factor is that USB-C and Thunderbolt docks arrived in 2015, so it probably didn’t make sense to introduce a whole new dock for the Exx40 and above models only to replace them again a few years later.

@dainova  If you’re looking at docks that connect via USB, then first be aware that they will not charge your system, since USB-A “regular USB” does not support sending power in that direction or carrying anywhere near enough power to run a laptop. USB-C does, but your system doesn’t have that. And second, USB-A docks and even some USB-C docks rely on “indirect display” technology called DisplayLink, not to be confused with DisplayPort, and that technology can have some drawbacks that can be significant. I wrote about those in the post marked as the answer in this thread. So I wouldn’t recommend that setup unless you have a system that doesn’t support any other dock options, but that isn’t the case for you.

And yes, power buttons are an issue because there’s no industry standard for an external power button, so that only works with equipment from the same vendor. And even there it won’t work with all laptops. Dell and Lenovo docks with Power buttons can only use them with Dell and Lenovo laptops, respectively, but not even ALL Dell and Lenovo laptops, because Dell and Lenovo haven’t added the necessary firmware support for a dock power button onto all of their laptop models. They both only seem to add it to their laptops in their business lines.