Hi, BirdInt'Hand!
Thanks for reaching out to Microsoft Community and posting your inquiry. I see you wish to extend your charging cable. To be sure we are on the same page, please allow me to ask questions so I will understand the situation better. Do you have a Surface 3 charger with a USB port on the brick? Do you wish to use a different wire to plug into its USB port to charge another device or the Surface 3? If possible, can you post a photo of what you wish to achieve and label them in the photo? This would really help us out.
Looking forward for your response!
Kind regards,
Janette_Z