Second screen for EL D5530 + Dell USB-C Mobile Adapter - DA300 - 4K?

@ddeconin2  Please recheck that system model.  Dell has never made a laptop called the "D5530".  I see you posted this in the Precision section, so do you perhaps have a Precision 5530?  If so, you would only be able to run 4K at 30 Hz through the DA300, not the standard 60 Hz.  Running 4K 60 Hz through the DA300 requires a system that supports DisplayPort 1.3/HBR3 or better over USB-C, and your system only supports DisplayPort 1.2/HBR2 over USB-C.  The first Precision 5000 Series model to support something newer was the 5560, which supports DisplayPort 1.4 (still HBR3).  Note: The signal from the system is always DisplayPort.  If you use the HDMI or VGA outputs on the DA300, a signal converter chip in the DA300 switches the signal type over.

In terms of alternatives, a simple USB-C to DisplayPort cable would allow 4K 60 Hz from your system, or USB-C to HDMI 2.0 if your display doesn't have DisplayPort.  The reason they would work but the DA300 wouldn't is because the DA300 sets up the USB-C link to carry both video and USB 3.x data, and doing that cuts video bandwidth in half -- and a half-bandwidth link isn't enough to run 4K 60 Hz from a DisplayPort 1.2 system.  By comparison, a simple USB-C to DP/HDMI cable allocates all high speed lanes in the USB-C connector to video, doubling bandwidth compared to the DA300.

But if you want a multi-function solution, the only way to run 4K 60 Hz simultaneously would be with a Thunderbolt dock like the WD19TB.  That can actually run dual 4K 60 Hz displays if you cable the displays within the requirements laid out in its user guide for DisplayPort 1.2/HBR2 systems.  Of course that isn't meant to be portable like the DA300 is, and it's more expensive, but it also offers more functionality, including coming with a power source so that you can charge your system from the WD19TB, thereby freeing up your system's own power adapter to be kept as a dedicated travel charger or perhaps parked somewhere else you spend a lot of time, as opposed to you having to unpack and repack it every time you come and go from your desk.

But for portable multi-function solutions, the only way you could run 4K 60 Hz and other items simultaneously would be with a device that supported 4K 60 Hz but only ran USB 2.0 data speeds for its other functionality, since USB 2.0 doesn't require cutting video bandwidth in half to carry.  But I don't know of any adapters like that.