DC LVDT Excitation voltage to NI CompactDAQ
Neither the manual nor the datasheet are particularly clear about powering the sensor. It's quite possible that at some voltages, it doesn't need the full 25mA.  But without finding that information in the datasheet, then even if the sensor seemed to work with lower current, we'd never be sure it was going to be reliable.

So you need to find a way of providing the 25mA at between 10 and 30V. Do not try to control the voltage of your DC power supply with a pot/divider, they can only regulate voltage at negligible load, if you want to regulate the voltage you should use a suitable voltage regulator IC. But unless I am misunderstanding the datasheet, you don't need to regulate it at all, 12V is between 10 and 30, so you can just connect it up.

Introducing a second ground is unlikely to be a problem, for two reasons:


Many AC/DC converters one can buy are isolated anyway. Double check yours, but it probably doesn't introduce a ground.
The manual states that the sensor input and output are isolated, so it wouldn't be a problem if they used different grounds.