High frequency transformers provide galvanic isolation between the primary and secondary sides of power electronic converters. The parasitic parameters of the HFT affects the converter control parameters especially its resonant frequency (for resonant converters). Most HFT design and optimization methods in literature often ignore the parasitic capacitance during optimization. This paper investigates the impact of the parasitic capacitance and the electromagnetic parameters of two already optimally designed 20kW, 10kHz, 208/208V HFTs (with different design parameters and power densities) used in a DC-DC series resonant converter. An FEA-based simulation of the electrostatic and electromagnetic parameters of the HFTs and experimental measurements are presented. The effects of the parasitic capacitance on series resonant converter's resonant frequency is investigated. The simulation and experimental results show that for series resonant converters, the parasitic capacitance severely affects their resonant frequency values. This effect need to be taken into account during the design and optimization of the HFTs.