Is replacing the power adapter jack possible? Would that mean unsoldering it from the mainboard, finding a replacement jack, and then soldering the jack into the mainboard? That sounds pretty adventurous.
Yoga 720-13IKB (Type 81C3) Laptop (ideapad) - Type 81C3
Model Name: 81C3
Mfg Date: 17/10/09
MTM: 81C3000LUS
Page 50, 51 of Hardware Maintenance Manual shows the power adapter jack.
For Lenovo YOGA 720-13IKB, the AC power adapter jack is compatible with Type-C USB 3.0 devices.
Service Manual
https://download.lenovo.com/consumer/mobiles_pub/yoga720-13ikb_yoga720-15ikb_hmm_201702.pdf
User Guide
https://download.lenovo.com/consumer/mobiles_pub/yoga720-13ikb_yoga720-15ikb_ug_en_201702.pdf