Dr. J
I suggest you quickly try out your new/old power pack with a train on a loop of track. I'm afraid you may be disappointed in your ability to control your locomotives at slow speed.
The power pack you show was designed to control HO locomotives with open frame motors - motors that typically drew 0.5 amps or more running. It uses a variable resistor - rheostat - to control the voltage going to the locomotive.
The downside of rheostats is that the voltage drop (voltage subtracted from the motor) is the product of the current drawn by the motor times the resistance added by the knob setting. The speed of the motor depends upon the voltage reaching it.
Today's N scale locomotives typically use 0.1 to 0.15 amps running. So the same rheostat resistance (based on knob setting) will only cause 1/5 to 1/3 the voltage drop that would occur with an old HO locomotive. There will often not be enough resistance, even at the lowest knob setting, to slow your N locomotives to a slow switching speed.
Newer power packs, like the MRC Tech series, while having the plastic cases you despise, control the voltage to the motor through a transistor circuit instead of a rheostat. This gives you direct control of the voltage regardless of the current being drawn by the motor.
Hence my recommendation to try your power pack for suitability while it is still possible to return/exchange for something that will give you the control you need. If the pictured pack works well for you, then disregard all I have said. But I will be very surprised. Towards the end of the "copper case" line, MRC did make their power packs in N variants with a higher value of resistance for the rheostat. These were marked with an "N" at the end of the model number or name.
yours in having fun with trains