I have encountered this voltage-mixing in the past and it can be easily solved if you understand the issues/principles involved.
Please visit this following post to get more details, although it was written for an OpenCM-904 controller, the same approach applies for all ROBOTIS controllers.
You will need to create ONE custom X3P DXL Power Cable, see this post:
and ONE custom X3P cable (with VDD cut off) to serve as an “electrical isolation” between the 5V DXLs and 12V DXLs (i.e. for the 2 Power Circuits), and as an “electrical bridge” for the Control Circuit which should be common to ALL DXLs and connected back to the OpenRB-150.
Please check these posts first. And then if you have more questions, just ask away back at this current post.
UPDATE - 7/28/2025
Please read up on this recent post too, there are other devices and options for voltage conversions and DXL Control nowadays, IF YOU NEED TO USE ONLY THE 12V POWER SUPPLY and can do some wire soldering.
