There is no such adapter as far as I know. As for building -- well, how good are your electronics skills?
Just sell the old one. You'll get enough money to buy two new ones from a 3rd party. The beauty of the USB-C port is that it's a standard. Sure, you can use Apple's big fat heavy 87W charger. However, I get through the day with a 45W charger. Here are two very well tested ones:
https://www.amazon.com/dp/B01D8C6ULO (Anker)
https://www.amazon.com/dp/B01ET762XS (iVoler)
In a pinch, I've charged my MBP with a 40W Nintendo Switch charger!
https://www.amazon.com/dp/B01N7RUZ49
Great options. In fact, I have the Anker already in my shopping cart, just waiting for my Lumsig (https://www.amazon.com/Lumsing-Charger-Foldable-Macbook-Compatible/dp/B01I1OIO4A) charger to arrive. It says 48 Watt, delivering only 30W to the USB-C port, so I hope that I will be able to work, even if the battery doesn't charge. But if it doesn't, I'll get one of the options you linked. The iVoler looks cool.