You've been in this situation:
Running around the house, looking for the DS charger but all you find is the broken one

Today, I'm going to teach you how to make a USB one that you can plug into any old USB port.

As long as the cable is intact, you can use a broken DS charger

TO AVOID FRYING YOUR DS, FOLLOW ALL STEPS CAREFULLY

Preparation

You will need:
Soldering Iron
Multimeter
Tape/[Heatshrink+Lighter]
A USB cable (doesn't matter what brand)
DS cable
Utility knife/scissors

Nice to have:
Alligator clips
Helping hands holder tool
Wire stripper

Step 1: DS Cable Polarity

Finding DS cable polarity

1. Cut the DS charger wire to the desired length from DS plug
2. Strip the cable until you see exposed wires
3. Set your multimeter to continuity mode (if + and - are touching, it makes a beep)
4. Hook up one wire to your multimeter (Aligator clip recommended)
5. Hold the DS plug and test both of the contacts INSIDE the connector (Helping hands tool recommended)
6. When The multimeter makes a beep, write down the wire that corresponds to the contact (you will need this later)
7. Repeat steps 4-6 for other wire
8. Once you have both wires corresponding to a DS plug terminal, Use the image below to determine wire polarity (you will need this later)

DS Plug Polarity Image

Step 2: USB Cable Polarity

Follow parts 1-8 of step one with a USB cable, using the polarity image below:
NOTE: Ignore the two MIDDLE contacts of the USB plug as those are not power

USB Plug Polarity Image

Step 3: Soldering

Now that you've got 2 wires from both cables marked as positive or negative (+ or -), we can now go onto the soldering
NOTE: If you are using heatshrink, apply this now to the wire.

Now, solder the POSITIVE USB wire to the POSITIVE DS wire and apply tape/heat heatshrink
Then, solder the NEGATIVE USB wire to the NEGATIVE DS wire and apply tape/heat heatshrink

Now, Wrap tape around the entire joint for durability and test it out!

Congratulations! You've made yourself a USB DS charger!