The power-fan canister has LEDs and its own power switch and power outlet. Each 12-drive or 24-drive shelf has two of these canisters.
The power supply is functioning correctly.
The power supply failed, the AC switch is turned off, the AC power cord is not properly installed, or the AC power cord input voltage is not within margin (there is a problem at the source end of the AC power cord).
The power supply or the integrated fan has a fault, or there is no input power to this power-fan canister, but the other power-fan canister is operating.