What creates pressure in the outlet line of hydraulic pumps?

Resistance to flow creates pressure.

load created or Mechanical action due to inlet creates pressure in the outlet line of hydraulic pumps

About 120 bar rated  &   (180 - 200 )bar  Maximam

In the outlet of pump system creates pressure.

Pumps produce current and resistannce creates pressure

Pressures in the out and in the lines downstream are given by the pumps, particullarly the outlet line is more exposed to the back pressure in the circuit. 

Possitive dispacement force  create the pressure inthe Outlet line, actually mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line of the pump

The load or actually the resistance of the system including the load

load inlet pressure from the pump 

Hydraulic pump create only high force flow,after that in the hydraulic circuit system restricted high flow force it's created pressure like relief valve in the hydraulic system inbuilt control valves.

It is the actuator like working hydraulic cylinders or drive motors creates pressure in the outlet of hydraulic pumps.