I'm currently looking into Thunderbolt 3 Docks for my newly aquired Dell XPS 9560. What I found was that Dell's original Thunderbolt Dock TB16-240W comes at a steep price of over 450€ here in Germany. For that price you get quite a lot of connection options, but often you don't need as many and get by much cheaper. Here are some alternatives if you don't need that excessive bouquet of options.
Dell's Thunderbolt Dock TB16-240W (450€)
Goodie 1: TB3 peripherals will be powered with 60W and Dell's own laptops even with 130W (above TB3 spec which is 100W).
Goodie 2: Up to three 4k displays may be served
2x USB 2.0, 3x USB 3.0, TB3 connection (USB-C), Audio in and out and GBit Ethernet. Graphics ports are Mini Display-Port, Display Port, HDMI Type A and VGA.
Here are some alternatives:
Dell's USB-C Docking Station WD15 - 180W (used on ebay for around 120€)
Caveat 1: No Thunderbolt Dock, only USB-C
Caveat 2: Only one single WHQD @ 60 Hz display supported
USB-C (USB3.1) connector to host, 2x USB2.0x 3x USB3.0, Audio in and out and GBit Ethernet. With HDMI, Mini Display Port and VGA connection.
Dell's Thunderbolt Dock TB15 (used on ebay for around 200€)
This dock is said to have some issues, please see the Dell forum for more info http://en.community.dell.com/support-forums/laptop/f/3518/t/20002660 2xUSB 2.0, 3xUSB3.0, HDMI Type A, Display Port, GBit Ethernet, Audio in and out, VGA, TB3 (USB-C), Mini Display Port
HP Elite 90W Thunderbolt 3 Dock (200€)
Goodie 1: Two external 4k (2160p) displays possible
Goodie 2: Host charging and charging of a secondary device (15 W) possible
1xUSB-C, 3xUSB3.0, 1xUSB3.0 powered, 3x Display Port 1.2, 1xVGA, Audio in and out and Gbit Ethernet
Plugable TBT3-UD1-83 Thunderbolt 3 Docking Station
Caveat 1: Only one additional display out of the box possible. More displays only via adapter (USB-C to HDMI/DVI/VGA).
Caveat 2: No host charging
Caveat 3: No Linux support
2xUSB 3.0, Display Port,1x USB-C 3.1 Gen1, 2x USB-C 3.1 Thunderbolt 3 (one port is for host connection), Audio in and out and Gbit Ethernet
Further research required: