A variable displacement pump system, comprising: a variable displacement pump disposed in a main line and configured to receive a low pressure fluid and to output a high pressure fluid; a pressure port disposed in the main line downstream of the variable displacement pump configured to port a portion of the high pressure fluid from the main line to a bypass line; a pressure regulating valve disposed in the bypass line configured to bypass a portion of the high pressure fluid from the main line to control a pressure of the main line based on an adjustable regulating set point of the pressure regulating valve; a first controllable valve operatively connected to a metering mechanism disposed in a secondary branch of the main line upstream of the pressure regulating valve configured to modulate a pressure of the secondary branch to control the adjustable regulating set point of the pressure regulating valve; a mechanical linkage operatively connected to the variable displacement pump configured to be driven by a pressure actuated piston to control displacement of the variable displacement pump; a second controllable valve operatively connected to the pressure actuated piston configured to supply a pressure to adjust the position of the piston; one or more sensors operatively connected to sense at least one of a position of the pressure regulating valve and/or a pressure of the main line and configured to output a respective signal indicative of the position of the pressure regulating valve and/or the pressure of the main line; and a controller operatively connected to receive at least one of the signal indicative of the position of the pressure regulating valve and/or the pressure of the main line, wherein the controller includes machine readable instructions configured to cause the controller to: control at least one of the first and/or second controllable valves (122, 132) to achieve an adjustable regulating set point position of the pressure regulating valve; and adjust a position of the pressure actuated piston to drive the mechanical linkage, varying displacement of the variable displacement pump based on at least one of the signal indicative of the position of the pressure regulating valve and/or a pressure of the main line. a variable displacement pump disposed in a main line and configured to receive a low pressure fluid and to output a high pressure fluid; a pressure port disposed in the main line downstream of the variable displacement pump configured to port a portion of the high pressure fluid from the main line to a bypass line; a pressure regulating valve disposed in the bypass line configured to bypass a portion of the high pressure fluid from the main line to control a pressure of the main line based on an adjustable regulating set point of the pressure regulating valve; a first controllable valve operatively connected to a metering mechanism disposed in a secondary branch of the main line upstream of the pressure regulating valve configured to modulate a pressure of the secondary branch to control the adjustable regulating set point of the pressure regulating valve; a mechanical linkage operatively connected to the variable displacement pump configured to be driven by a pressure actuated piston to control displacement of the variable displacement pump; a second controllable valve operatively connected to the pressure actuated piston configured to supply a pressure to adjust the position of the piston; one or more sensors operatively connected to sense at least one of a position of the pressure regulating valve and/or a pressure of the main line and configured to output a respective signal indicative of the position of the pressure regulating valve and/or the pressure of the main line; and a controller operatively connected to receive at least one of the signal indicative of the position of the pressure regulating valve and/or the pressure of the main line, wherein the controller includes machine readable instructions configured to cause the controller to: control at least one of the first and/or second controllable valves (122, 132) to achieve an adjustable regulating set point position of the pressure regulating valve; and adjust a position of the pressure actuated piston to drive the mechanical linkage, varying displacement of the variable displacement pump based on at least one of the signal indicative of the position of the pressure regulating valve and/or a pressure of the main line. control at least one of the first and/or second controllable valves (122, 132) to achieve an adjustable regulating set point position of the pressure regulating valve; and adjust a position of the pressure actuated piston to drive the mechanical linkage, varying displacement of the variable displacement pump based on at least one of the signal indicative of the position of the pressure regulating valve and/or a pressure of the main line.