Runninrep,
Suggest viewing the following Bachmann video the first time with sound turned off as the misnomers and inconsistent nomenclature used may confuse you.
Click Here to view video
In the video you will see why only one red power wire is included in the
Nickel Silver E-Z Track Expander Set
Short Red Power Wire - Old style (N, HO, On30, G Scales)

Model/Item 44219 16V DC Multi-Accessory Power Supply
The Multi-Accessory Power Supply is covenant but not necessary to use. A less expensive method is to splice the red power wires to wires of a Wall Wart power supply/adapter/transformer with an output rated 16 volts AC and 1 Amp (1000 mA). Remove the Wall Wart’s plug at wire end, splice and solder its wires to the red power wires. There are many ways to connect without soldering. Using screw terminal blocks is one. Google
connect small gauge wires without soldering to see more methods