from the picture you have here, That I see you have a
Wahl 8554 Wahl Alpha cordless clipper. but you stated the model 9918-6171 Groomsman Beard and Mustache Trimmer model, You need to be sure of what model you have. He are the two picture of each model. if this is correct, Mannys Sharpening has the charger for this cordless clipper, I had the same problem and he sent me one it took about 2 weeks for delivery.
The clipper on your Left is Wahl 9918
This clipper is the Wahl Alpa 8554 cordless
Call Mannys Sharpening he has all the replacement charger for Wahl.
323 263-4697