I admittedly haven't tested this on a system that supports MAC address passthrough but does not have its own built-in NIC, but the PowerShell command below will all enabled network adapters on the system and their MAC addresses.  You can omit the Computer parameter if want to run it against the local host:

gwmi Win32_NetworkAdapterConfiguration -Computer TargetPC | select Description,MACAddress

As you'll see, there are often several MAC addresses on a given system due to virtual interfaces that exist in Windows, but if you find a pattern to the name of the interface and/or the MAC Address itself, you can add the "where" cmdlet to filter only what you want.  If the above command doesn't work at all for your systems, Dell has the Dell Command suite of applications, part of which involve command-line tools that can be used to read and modify BIOS settings, so if you see the MAC Address you want in the BIOS, you might be able to grab it with the correct Dell Command application.

Thank you. I found the solution to my problem here:

https://www.dell.com/community/Enterprise-Client/Dell-Dock-D6000/m-p/5183399/highlight/false#M5608