Reddit mentions of 1 X Solid Solder 0.3mm Dia Flux Core 63% Tin 37% Lead Long Wire Reel

Here is how NASA would splice that wire :). All you need is a decent soldering iron and a little bit of solder. Do it outside, especially if you are using lead based solder. A little heat shrink tubing and you can have that cord back in working order, even if it's a tiny bit shorter :).

There should be two wires inside that cord though: one for positive, and one for negative- make sure not to let these wires touch each other!