Hi, I own a Transformer Book T100TA and faced the same problem too.
I have been using 3rd party charger since my original cable damaged from a tight bend.
I have been searching the original charger for a while and finally decided to dissect the original usb connector since the original charger is so expensive. The I found the usb connector is so unique that you can’t simply replace it with an ordinary usb charging cables. Sort of similar to iphone charging cable. If you have a good soldering skills, you might be able to build one yourself as it’s considered as a technique called micro-soldering. You would required to slice open a micro usb connector and solder the smd resistor into place and seal up everything. Hope this helped.