Originally Posted by froyd
So, it would seem the flash voltage is not a plainly advertised spec.
No. There is a ISO definition of 24V, but that only came decades after electric flash triggers had already been established. If violated the preceding practice, which used anything between 60V (bulb batteries) and grid voltage (by local standards of the maker), and it was not future proof either - 24V is inherently unsafe for digital circuits (whose safe limits are somewhere between 3V and 15V). So the ISO standard may well be the least used trigger voltage around.
PC sync makes no difference, by the way, the actual trigger system is the same. But it is free from the risk of the trigger contact sliding across any of the digital ports of the TTL system.