The factors that affect the compatibility of Engine Generators with Switchmode Rectifiers are identified. The performance of the input sections of active Power Factor Corrected (PFC) Rectifiers, that affect compatibility, are examined including turn-on characteristics, input impedance and control loop stability. Recommendations are given for the characteristics of Generators to assure stability. An overview of experiments conducted on three different 3-phase rectifier systems operated with both AC mains and Engine Generator sources is given. Typical power system designs to address rectifier input harmonic distortions reflected to the source (AC Mains or standby Generator) are reviewed. The cost savings and reliability of the AC power systems using conventional transformers in lieu of mitigation transformers, when well designed active Power Factor Corrected (PFC) Rectifiers are used, are presented for power systems backed up by standby generators.