This work examines the gate oxide ruggedness and underlying failure mechanisms of commercially available large-area 1.2 kV 4H-SiC power MOSFETs from multiple vendors. Both gate leakage current and time-dependent dielectric breakdown (TDDB) measurements are performed at various voltage stresses with temperatures between 28°C and 175°C. While some vendors show promising gate oxide reliability results such as low gate leakage current ( 100pA) and >106 hours lifetime at 175°C with VG=20 V, anomalous gate leakage current behaviors and TDDB characteristics are observed for other vendors. The anomalous gate oxide reliability measurement results are related to the pre-existing gate oxide defects and interface traps. Gate leakage current measurements at different temperatures reveal insights into the oxide quality. The authors also observe that constant-voltage TDDB measurement can greatly overestimate the oxide lifetime when a significant amount of extrinsic oxide defects exist before the measurements.