Power supply interruptions (blackouts) that can cause loss of network connectivity
Power supply issues (brownouts, platform wedges) that can cause loss of platform operations requiring a manual intervention.

A simple UPS should be procured from an outside vendor that can supply sufficient power (watts/VA) to feed the platform, and sufficient capacity (watt/VA-hours) to keep the platform running for at least 15-30 minutes.
Platform maximum power requirements from the hardware specifications:
NFX150 – 150 watts
NFX250 – 250 watts
NFX350 – 250 watts
 
Power output from the UPS should be at least 25% higher than required power for the platform.
Switchover time should be <50ms. 

A site survey performed by a Licensed Electrician is recommended.
 

All NFX platforms should be connected to an Uninterruptible Power Supply to reduce risk of:

• Power supply interruptions (blackouts) that can cause loss of network connectivity
• Power supply issues (brownouts, platform wedges) that can cause loss of platform operations requiring a manual intervention.

 
This is considered best practices for standalone platforms installed in “retail locations” and/or at end-customer sites without onsite technical support.

NFX250 Network Services Platform Hardware Guide | Juniper Networks