Hello Eric, in dual power supply deployment of the HPE FlexFabric 5900AF switch, if one of the hot-plug redundant power supplies is disconnected from the power line the other power supply is able to sustain the switch's operation...in other terms:
If the switch has two power supplies, removing one power supply does not affect the operation of the switch. If the switch has only one power supply, removing the power supply powers off the switch.
Clearly you will lose the redundancy...but considering that your whole powering-off / powering-on procedure will last just few minutes the risk of issues during that interval is reduced.
Normally operating the Switch with just one PS is not a best practice.
Read more
here.
Edit: use
display power to assess the status of your two Power Supplies pre/post procedure.