Basically not more complicated than splicing wires, a greater reason for this is to make using AC to DC transformers we see all of the time less mystifying. The main limitation is that you need to have a US adapter with the same DC output, or you risk frying whatever you're about to electrify. DC power adapters can be used to charge or power anything that uses DC power, including IDY electronics like the Arduino, or basically anything else in your house that uses a DC power converter. As for this instructable? I made it at TechShop!
1 - Foreign power adapter with the right phone connector
1 - US power adapter with the same voltage as the foreign adapter
1 - Wire strippers
1 - Bit of electrical tape
Basically you're going to:
1. Check to make sure the specks work
2. Splice the phone connector to the US adapter
3. Charge your phone!