The following models are available on the market: ACX3 30 30 mbar ACX3 30 50 mbar ACX3 40 30 mbar ACX3 40 50 mbar ACX3 40G gas cartridge
I assume someone has used the manufacturer's article number as the model name. D probably stands for Dometic. So ACX 3 30 and ACX 3 30-D would be the same thing. There is something wrong with the item ACX 3 30-D anyway, it is also much more expensive. I assume it's a generic product in the range.
When ordering, make sure the gas pressure is 30 or 50 mbar. This second most important point is not properly declared (if at all).