About using the “power” of the GPIB, I made my own Arduino-Nano based GPIB-to-USB converter and found out the hard way that there are quite some voltages coming from the GPIB.
I recently moved my Solartron 7150+ multimeter to a shelf to get more space on the bench and as the rear wasn't easily accessible anymore I started to leave the GPIB connector permanently in. Soon later, I noticed that my GPIB-to-USB adapter stopped working and the only way to revive it was to re-upload the program. It worked fine for a day or two and then was dead again. I spare you the lengthily troubleshooting.
In the end it turned out that when removing the USB power from the Arduino by turning my PC off, but with the Solartron still powered on, the ATmega328pb chip would be lingering sort of half-dead, just getting a little bit of power ( 2.2V ) coming in through its IO lines from the GPIB termination resistors. This state would cause the flash memory to corrupt in no time and the only way to get it working again was to re-upload the program into the flash memory.
The solution was to program the chip fuses to enable brown-out detection (BOD) on the ATmega328pb, which was an adventure in itself because that chip (used by Chinese Arduino clones) is not really supported by the Arduino IDE when it comes to setting fuses and reloading bootloaders... In the end I managed to get around this and program BOD for 4.3V so the chip stays reset until the supply voltage (5V from USB) exceeds that threshold. You can see the story on this here
https://youtu.be/DAS1KVU_FaA and there are a few other GPIB videos on building this adapter
https://youtu.be/RaLirRvSngk and using it to automate measurements with a DPS5005 programmable power supply module:
https://youtu.be/FXv_CFu6FPw.