Can you give me an example (link, etc) of the type of engine that you are talking about, which does not have an alternator?
I would expect many outboard motors to use the same type of alternator that motorcycles generally use: Permanent magnets built into the flywheel, surrounding a stator which is connected to a voltage regulator that is designed for this purpose, with the whole assembly being built into, or bolted directly onto, the crankcase. It's still an alternator ... just not the separate pulley-driven type that you may be accustomed to from automotive use.