Howdy elyan,
Normally one can find drivers for serial-controlled instruments like power supplies by visiting the Instrument Driver Network (IDNet) as outlined in this KnowledgeBase article. However, it doesn't seem like your particular B&K power supply in particular is listed there among the available B&K instrument drivers.
Looking into it a bit further, I did find a BK 1785A manual on this page. On page 14 of this manual, it mentions that it requires a separate kit to use the RS-232 interface option on this power supply. It says this kit comes with the necessary hardware, software, and additional instruction manual, so assuming you have this additional kit, you would need to reference this additional instruction manual and develop your own instrument driver.
I don't know what quality of driver you want to develop, but the following article outlines and good practices to keep in mind when developing instrument drivers: DeveloperZone Tutorial: Developing LabVIEW Plug and Play Instrument Drivers
Alternatively, you could use something simpler like the Basic Serial Write and Read from the NI Example Finder if you have just one or two commands that you send to the power supply.
I hope this helps! Best of luck with your application, and have a great day!
Warm regards,
pBerg
