Low inertia has become a great concern for the power grid with high inverter-based resources (IBR), such as solar and wind power generation systems. Therefore, synchronous condensers have been used to enhance the inertia level of the system. However, only a limited number of synchronous condensers can be installed due to their high costs. Thus, gridforming (GFM) inverters have been proposed as a promising alternative method to provide frequency support with simulated inertia to achieve 100% renewable penetration in the future. In order to provide a cost-effective adoption strategy for frequency support, a comparative study between synchronous condensers and GFM inverters has been performed through extensive simulation studies. The simulation results show that both strategies can reduce the rate-of-change-of-frequency (RoCoF) and enhance the frequency stability, and the combination methods with both synchronous condenser and GFM inverters can achieve a cost-effective transition plan for the bulk grid