ESXi uses lm_sensors for hardware monitoring, and this tool needs a lot of config-tweaking. Above all temperature-readings (but sometimes voltage too) are off-scale, and deliver wrong data. This can be corrected using lm_sensor configuration file, where you can define some "correction factors" for individual sensor-readings, i.e. multiplication by (-1) if positive Voltage is reported as negative, or adding constant +50 to get proper temperature values. I recommend to check lm_sensors forum and your hardware...
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