A high power density non-intrusive magnetic field energy harvester (MEH) and dual-output power management system are proposed in this paper, targeting at widely distributed online monitoring devices for HVDC IGBT converter valves. IGBT converter valves contain sufficient kHz magnetic field due to the periodic switching of IGBT devices. High frequency MEH has the advantage of high power density. An improved I-shaped core is proposed with equivalent permeability studied and engineering practical design guidance for magnetic flux convergence. Furthermore, a wide input range dual-output power management circuit is proposed for wide magnetic intensity variations. A dual energy flow strategy is adopted with combined boost energy conversion path and buck-boost energy conversion path for better utilization of harvested energy. PCB planar coils and PCB based power management system are packaged inside the I-core to eliminate the electromagnetic interference on the low power circuit. The power density of the proposed MEH reaches to 1.89 mW/cm³ under magnetic flux density amplitude of 500 μT at 1500 Hz. The maximum efficiency of the boost path in the charging process reaches to 94.1% and the average efficiency for buck-boost path in the discharging process from 4.0 V to 0.3 V is 68.0%.