A B757's EICAS alerted 'STBY INVERTER' as a status message. The crew investigated the alert and were not informed that the STBY inverter had failed leaving the aircraft with no backup STANDBY AC power source.

Narrative

B757 (non ER) transcontinental flight. About 30 minutes after departure; at top of climb (FL350) we noticed a hot 'electrical' smell. Flight attendants called to say they noticed it too. No fire; no smoke and the smell dissipated in a few minutes. At about the same time; we observed a status message on the EICAS 'STBY INVERTER.' No other indication (bus off light; discharge light; etc) of any kind. All indications and operations (other than the status message) were normal. Manual says status messages are for ground operations; dispatch; only. No in-flight pilot actions are required or necessary. Also states that this message indicates that the inverter is putting out higher voltage than usual. Talked to Maintenance Engineering; they had no additional ideas; except to ask if there was a battery discharge light. There wasn't. Asked if the status message would go away if the problem resolves itself. Maintenance Engineering didn't know. Also let Dispatch know what was going on. Tried to understand what might be happening with the inverter; but chose not to troubleshoot; pull breakers; etc; as that is not policy; and there are no schematics or other information in any manual to refer to in-flight. First Officer and I discussed the ramifications of a problem with the inverter (standby aircraft; Cat III landing; etc.); over the course of the rest of the flight. Again; no relevant information available in our manual; the QRH; MEL; etc. Upon landing at destination after an otherwise uneventful flight; spoke at length with the Mechanic. The standby inverter had failed completely. Here are the real issues: 1) Information in our manual regarding that particular status message is incorrect. It wasn't putting out high voltage; if they failed completely. 2) Loss of the only alternate method of producing standby aircraft power (not an ER airplane) should be a caution message; not just a status message. 3) The manual needs to include at least the most rudimentary information (schematics; etc.) about systems. Lots more I could add; but hopefully you get the point. Even though all procedures; checklists; etc were followed exactly; and all information sources were consulted. I feel that this crew was left somewhat in the dark regarding what was actually happening and what action to take.