Precision 7520 - Docking Station and external power supply

Hi,

I still have an old PR03X docking Station, will this work with the Precision 7520?

What about the new Thunderbolt Docks - I read somewhere that I would still need  to plug in an additional power supply for the Precision models since they use so much power (180W) even when they are connected to the Dock??

If that is true, can't I simply buy some generic USB-C Docking Station, i.e. what does the Precision Laptop do in regards to power supply from USB when I have already the regular power supply plugged in? Hopefully nothing in regard to charging from USB-C? Or how does that work?

Thx!