The more reliable devices aren't cheap (unless you could find one used, which I've not seen very often).
The
Enttec Open
DMX (Or a "compatible" version of it) works, but if your computer locks up for a second, your lights will stop and possibly freak out.
The
Enttec DMX USB Pro (or "compatible") is more reliable, it internally buffers the
DMX packets your computer sends, so if your computer stops, you lights might stop changing for a second, but it won't result in them freaking out and going to a weird color or something along those lines.
The least reliable device you can
build is $10, a cardboard box with a USB to RS485 converter that you buy from china, connected to a female
XLR plug sticking out the side.
I dunno how unreliable it is compared to the
enttec open, I wouldn't use it for anything more than bench testing,
etc.