Historically, with the lead of conventional generation, the inertia of power systems has been taken for granted, but as these evolve with increased penetration of inverter-based resources, new questions arise, particularly on which are the adequate solutions to maintain or improve the system reliability in this modern scenario. Various technologies are available to overcome the lack of inertia, avoiding high frequency changes and deviations in the power system. Among these technologies, synchronous condensers engendered from the conversion of alternators in decommissioned power plants, fast frequency response services, and virtual inertia systems are the most widespread. In this work, a comparative study between these technologies is carried out, based on an isolated system with low inertia and high penetration of variable generation, in which sudden load variations have been considered. The objective of this study is to deliver some useful conclusions, particularly for transmission system operators, about the differences, interchangeability, and the combinability of these compensatory technologies.