High-frequency resistance spot welding systems are considered. They have full-wave center-tapped output rectifiers. They find wide application in resistance spot welding, instrument making, electronic industry, nuclear energy and automotive industries. A feature of these systems is a significant influence of electromagnetic parameters of the three-winding transformer included in the system on welding current and power consumption. This three-winding transformer is replaced by two two-winding ones. It is shown that welding current and power consumption depend both on the modulus and the sign of the coupling coefficient of the magnetic leakage fields of these two-winding transformers. For reducing the power consumption of high frequency resistance spot welding systems, it is necessary not only to reduce the leakage inductance of two-winding transformers, which replace the three-winding transformer, but also to reduce the positive coupling coefficient of the magnetic leakage fields or increase the modulus of the negative coefficient