Analytical and numerical investigations of a mechanical system excited by a rotating unbalanced mass are presented in this paper. The model consists of a rotor driven by DC motor with limited power and an oscillator with stiffness changing periodically in time. Damping of the system is assumed in two variants as linear-viscous or non-linear which can produce self-excitation. Interactions between the energy source (inertial excitation), parametric and self- excitations for regular and chaotic motion are demonstrated in the paper. Amplitudes near the main parametric resonance, synchronisation phenomenon and transition to chaos are determined for the considered model.