Depends on how you describe "main power source" -
inverter? house
batteries?
charging source?
We have an AC
generator. If that goes, we have a large main
inverter.
If our main inverter goes, we have a couple of smaller backup inverters than can be used. We also have a number of DC-DC converters that can run and charge
computers,
GPS, etc.
If our house batteries go, we have the two start batteries that can be used. If they go, there is a small
battery in the dinghy…
We have several charging sources -
solar, two alternators, the main
charger, a backup
charger and a portable charger.
If absolutely everything goes, we plan on bartering
water (big watermaker) for use of someone's portable
Honda genset.
Absolutely everything going is pretty much an extremely low probability - an event that causes it would probably require abandoning ship as it went down.
Mark