Re: Power supply

Hi Reload, 

Greetings, 

• The QFX5100 is shipped from the factory with two power supplies. Each power supply is a hot-removable and hot-insertable field-replaceable unit (FRU) when the second power supply is installed and running. 
  
• You will need an working spare PEM to swap the Power Supplies position. If only one power supply is installed in your QFX5100 device, you need to power off the switch before removing the power supply.
  

Verify the status of PEM and also if the PEM airflow direction matches the chassis:

show chassis hardware | match Power
show chassis environment | match Power
show chassis environment pem

Caution:

Verify that the airflow direction on the power supply handle matches the direction of airflow in the chassis. Ensure that each power supply you install in the chassis has the same airflow direction. If you install power supplies with two different airflow directions, Junos OS raises an alarm. If you need to convert the airflow pattern on a chassis, you must change out all the fans and power supplies at one time to use the new direction.

Reference Links: 

1. Removing a Power Supply from a QFX5100 Device 
2. AC Power Supply for a QFX5100 Device 
3. DC Power Supply in a QFX5100 Device 

Hope this helps. 

Please mark "Accept as solution" if this answers your query.  Kudos are appreciated too! 

Regards, 

Sharat Ainapur