The growing demand of renewable energy sources (RES) such as solar photovoltaic (PV) and wind energy into power distribution networks has significantly increased the importance of power quality (PQ) enhancement due to issues like harmonics, voltage sags/swell and frequency fluctuations. Traditional power networks were not originally designed for such distributed, intermittent, and non-linear generation, and hence require advanced PQ mitigation techniques. Recent studies have presented a variety of solutions ranging from passive filters to intelligent control of active filters and custom power devices. It provide a comprehensive review of PQ enhancement methods, categorizing solutions into passive, active, and hybrid filters, along with custom devices like STATCOM and UPQC. Their work highlights critical research gaps, particularly the need for adaptive and intelligent controllers, hardware prototypes, and optimization-based filter tuning. Their simulation results demonstrate a significant reduction in total harmonic distortion (THD) and improved stability. The Multi-Converter Unified Power Quality Conditioner (MC- UPQC) for simultaneous PQ improvement across multiple feeders. Their study shows effective mitigation of sag, swell, and harmonic distortion, but also points to challenges in controller coordination, converter sizing, and integration with storage for practical applications. Taken together, the reviewed literature underscores that while UPQC, MC-UPQC are effective in theory and simulation, research gaps remain in practical implementation. These include adaptive and intelligent control under highly variable RES conditions.