These jump starters have a 12 to 18 amp hour 12 volt battery inside them.
They need ~ 14 volts to charge. You can hook them to a regular car battery charger on the 2 amp setting. Just hook the red to red and black to black on the alligator clips. You can use the 10 amp setting, but only charge it for an hour or so if it is a manual charger. An automatic charger will not overcharge it on any setting.
If there is an on/off switch, it must be on for this to work.
It can also be charged by your car's alternator. Just hook it to the battery terminals. This will take a while though.
If it has a ciggy plug receptacle, as most do, you can make a male to make plug, and turn it on and it will charge slowly whilst you drive.
I know you are looking for a regular wall wart charger like what originally came with the Jumper pack.
If the jumper pack you have obtained has not been charged in a long time, there is a good chance the battery within is no longer strong enough to jump start a car, so I recommend charging it by other means before spending the money on a specialized charger, then finding out the unit is not strong enough to do the job it was designed for.
The batteries within are easily replaceable and run 25 to 55 dollars.
I do not think we are allowed to post links to products here. Google "12120 agm battery" and click on the very top post. It will show you the likely battery inside the unit, and an acceptable charger right below.
