How to connect a voltage and current source?
It’s safe to assume that you can’t just join the two together.  If you want to disable both power supplies in an e-stop situation then you could use a 2-pole relay to interrupt both circuits.  Typically you’ll use normally-open contacts so that e-stop occurs if the relay is de-energised for any reason.  E-stop switches are then connected in series and should all be normally closed to keep the relay energised in. Or mal operation.