I would like to extend 1080P DP signal around 3m. He will use the combination of CS1922 + VB905 to output 2 monitors as Windows Extend mode. 

Is it possible to implement this scenario when VB905 without power adapter? 

You have to use power adapter in this scenario, and use DP 1.2 cable, because pin 20 which supply the power wouldn't connect wired.  

The reason power isn’t included in standard cables is because both source and sink devices are designed to provide power.  Captive, attached cables often include the power wire.  If it is desired， for example， that a particular source device utilize the power available from the mating sink device, then that Source device could include an attached or dedicated cable that carries the DisplayPort power signal.  Same could be applied to a sink device.

Below is the link of the pin 20 explanation.