sfpVoltage reports the internal supply voltage measured by the SFP transceiver plugged into the port identified by sfpIndex. Admins check this against the module's rated voltage range to confirm the optic is receiving stable power, since voltage drift can indicate a failing transceiver or connector issue. For example, an sfpVoltage reading drifting outside the expected roughly 3.3V range for that optic type would prompt an admin to inspect or replace the module.