Just bought a XPS 7390 (not the 2-in-1) and wondering which docking station I should use.
Specifically, I already have a WD15. Is it compatible?
If not, which dock would be the best (and cheapest) alternative if I want charging, a single HDMI and a couple of USB type A ports?
@sivanbhthe WD15 should definitely be compatible. Dell has a newer WD19 dock, but I don't think it's essential for using with the 7390, and if that's all you need, then the WD19's differences over the WD15 wouldn't matter. As long as the HDMI display you want to run is no higher than 2560x1600 at 60 Hz, then you'll be fine. If you want to run 4K 60 Hz, you'd need a Thunderbolt dock like the TB16 or the newer WD19TB.
@sivanbh charging will definitely work. Laptops that support being charged over USB-C ports use the USB Power Delivery standard to achieve that. That standard defines certain voltages, currently ranging from 5V to 20V, and the process involves the power source and the device being charged performing a negotiation. Basically, the initial connection always starts with 5V power for safety and for compatibility with devices that don't support USB PD, since "regular USB" has always used 5V (except some proprietary standards like Qualcomm Quick Charge). Then if both devices involved support USB PD, the power source advertises the voltage and amperage levels that it can provide, and the device being charged is allowed to request those if it wants. (Note: Technically the USB-C cable can also come into play here, because there are USB-C cables that support up to 3 amps, and USB-C cables that support up to 5 amps. These are sometimes called 60W and 100W cables, respectively, since 3A and 5A at the 20V max is 60W and 100W, respectively. Cables that support 5A have an "e-marker" chip embedded into them to indicate this, and the power source won't advertise more than 3A unless it sees that e-marker chip. So if you use a USB-C cable that only supports 3A, then you'll only get up to 3A, i.e. up to 60W if you're using 20V, even if both the power source and the device would otherwise support higher amperage levels.)
The result of this design is that you'll never have a power source that supports the USB PD standard "force" a device to accept a higher voltage than it can actually use. Worst case you'll have a power source that can't charge the attached device because the power source doesn't support the power levels that the device being charged requires. For example, the XPS 15 models will only charge from a source that supports 20V. But even in that case, the device simply won't charge from that power source. The device won't damage the power source trying to pull more than it can provide, since the device isn't allowed to request anything that the power source doesn't advertise.