Customer recently purchased a JPSU-150-AC-AFI power supply unit along with the corresponding fans for use with EX3400 series switches.

However, after installing the PSU and fans into the EX3400P, while both the DC and AC (OC) LEDs on the PSU are green (indicating normal operation), the switch itself does not boot or power on.

From the document we could see that Ex3400-48P need JPSU-920-AC-AFO to power up the device.

https://apps.juniper.net/hct/product/?prd=EX3400

As per hardware documentation we could see that for Ex3400 the model 48T will support