Super Beginner Question on Soldering to a 5v to 12v USB step Converter
To save doing all of that, I would think it would be much easier if you just went and bought the other part of that Molex lead you have, for it to plug into, then you can just solder 2 wires from your Voltage Converter PCB and then solder them straight to the other Molex socket. Then you can just plug it in any time you want, and you still have your lead in good working order in case you want to use it for another project.

That is the way I would do it anyway.