Portable usb-c monitors don't work with MBP but with a dock it does?

[restock3eee]

Like Dell portable monitors. Connection is below. Some people state they work when a dock is used. One common model is dell P1424h. Does it not work because it isn't thunderbolt?

2 x USB-C/DisplayPort 1.2 Alt Mode (HDCP 1.4 / power up to 65W)​

 

[raythompsontn]

It is may be a power limitation on the MacBook port.

 

[Fishrrman]

Does just one of the displays work (with the other one disconnected for testing purposes)?

 

[rb2112]

For me, once in the past, the cable itself mattered (from macbook TB port to monitor). I also had a cheaper portable where it could not be bus powered, it needed a separate power input. And another where on bus power only, it was limited to 30% brightness.