Safely connecting a preamp powered by a benchtop DC power supply to a power amp
It should be fine. Just make sure that:


You select a sensible current limit at the power supply based on the
maximum current expected to be drawn by your preamp
You connect one the terminal of each output channel together: -25 GND---GND +25. In a benchtop power supply each output channel is isolated from the others.
Make sure not no mix up +25V and -25V :)