This article will answer most of your questions:
It also lists sync voltage limits for most cameras, brand by brand. To summarize from that article:
- Canon (350D and later models): 250V (Chuck Westfall)
- Nikon 250V (it's in the manual)
- Olympus 24V?
- Panasonic 15V?
- Pentax 25V
- Sony 24V?
The questions marks come in where more than one number is given, and the lowest one is taken to be on the safe side.
Then, measure your flash's sync voltage. You can look it up, but some models, like the Vivitar 283 and 285 can vary widely over the course of production. Some vintage 283s go up to 350V, some are in the <10V range.
I also wouldn't take the advice that any wireless trigger will work like a Wein Safe Sync. Some might. But wireless triggers, like camera hothsoes, also have a sync voltage limit. The Cactus V5 and Yongnuo RF-603II, for example, have a 300V limit. The Yongnou RF-602 and RF-603, otoh, have a 12V limit (hence the RF-603II).
You will also want to pay attention to polarity as well as the voltage.