I found that out when I used my previous 3600 on a Canon T90, and a hotshoe to PC adapter. It fried the flash port. That said is using the PC port on cameras with that safe? I have a Pentax 67 from the 90s using a PC port, and wonder if the 3600 would be safe for that? Id assume so, since that camera design goes back to the late 60s. I wonder if there is a hotshoe to PC adapter with a voltage regulator built in, to protect the camera?
Some people say that PC ports can stand higher voltages than hotshoes, and it may be true for certain cameras, but it is not reliable advice. I would guess that Pentax 67 could tolerate a higher voltage, being as you say a basically 1960's design with a makeover. Seems to have the same shutter with the 1/30 sec sync speed as the earlier 6x7 (which I have : horizontal cloth shutter) so it would probably have the same sync mechanical microswitch.
Also what is the advantage of using a 200 volt trigger vs a low voltage one? Should I upgrade my 3600 to a 544 to be safe? I believe the 544 is functionally the same as the 3600 in every way, other than the 544 has more output?
There is no advantage to a higher trigger voltage except that it is the voltage of the "raw" trigger circuit in the flash unit. Earlier flashgun designers saw no need to moderate it because the non-electronic cameras of the time could handle it. It is possible to get a bit of a shock off it, and some flashguns went up to over 250 volts. Later, the flashgun makers added a few more electronic components (quite cheaply after all) to moderate the trigger voltage down to below 24 volts and in some cases only 4-5 volts. There is a standard now that cameras should tolerate up to 24 volts, although it is not a compulsory standard - Canon have been known to advise a user of one of their recent cameras that it should not be subjected to more than 6 volts.
I have a 544 (which I like) but not a 3600. Looking at pictures of the 3600 they do look very similar, probably use the same battery pods and bracket, but the 544 does not have what looks like a remote sensor socket on the back of the 3600.