On MX100008 platform, when one of the feeds to one of the PEMs is interrupted, an alarm is not generated, only a message in the chassisd log:

CHASSISD_PEM_INPUT_FEED_STATUS: For PEM0: FEED A0 is not present 

An alarm is not generated if the installed PEM model is (JNP10K-PWR-DC2), because this model consists of two power supplies combined into a single unit (PEM), resulting in accepting four inputs, 2 for each power supply, so each PS has redundant inputs A0/B0 and A1/B1, having this concept in mind, an alarm wouldn't be raised for a single input absence on a single PS within the master power module, since from PEM perspective no input is absent.

An alarm should instead be raised when combination A0/B0 OR A1/B1 is off, this would equal one of the PEMs power supply absence which would translates into PEM loosing one of its inputs which logically should raise an alarm.

Further information about this PEM:

https://www.juniper.net/documentation/us/en/hardware/mx10008/topics/topic-map/mx10008-16-power-system.html#id-jnp10k-pwr-dc2-overview

An alarm is not generated if the installed PEM model is (JNP10K-PWR-DC2), because this model consists of two power supplies combined into a single unit (PEM), resulting in accepting four inputs, 2 for each power supply, so each PS has redundant inputs A0/B0 and A1/B1, having this concept in mind, an alarm wouldn't be raised for a single input absence on a single PS within the master power module, since from PEM perspective no input is absent.