I don’t have a strobe sync cord attached to my digital camera, instead my internal strobe on the digital camera will trigger the digital adapter which is sync cord attached to my old analog strobe. This is for point and shoot cameras that do not have a hot shoe for the strobe. Since I initially started shooting in Manual Exposure mode, my digital adapter is configured to NOT expect the preflash thus it fires when it sees my internal flash go off.
My Canon 300D used a Vivitar 285 and I shot it in manual exposure mode also and it did not lock the DSLR up at all. When I switched to programmed or auto mode it did not lock up either but then it fired one flash only and not a preflash + flash.
Using a safe sync is a wise decision to interface to the old strobes due to the differences in voltages on the new digital cameras.