In this paper, the performance of a novel structure of a 1.08 kW planar Linear Level Control (LLC) transformer with magnetic integration is evaluated and compared with the conventional top-up structure transformer. The developed planar LLC transformer has a number of advantages. The most significant advantage is that it adjusts the resonant inductance more effectively by changing the air-gap between the magnetic insertion and the transformer core. Compared to the conventional integrated transformers, the developed LLC transformer cannot only adjust the resonant inductance easily, but also achieves a 30% reduction in volume. The performance evaluation was conducted with the assisted modelling technique and verified with the impedance measurement result. Furthermore, three transformer prototypes were built and tested. An experimental efficiency comparison result is shown and analyzed.