We are working on having power supply redundancy and have recently purchased new power supplies for Juniper SRX1500 firewalls, wondering if inserting the new power supply requires system shutdown or is considered hot-swappable.

On SRX1500 the PSUs are considered hot-swappable.

https://www.juniper.net/documentation/us/en/hardware/srx1500/topics/topic-map/srx1500-overview.html

SRX1500 Firewall Field Replaceable Units Overview

Field-replaceable units (FRUs) are components that you can replace at your site. The power supplies are the only FRUs on the SRX1500 Firewall. The power supplies (if redundant) are hot-swappable. You can remove and replace the power supply without powering off the services gateway or disrupting the services gateway functions.