Dag

Dilute it rather than feed it harder. Pour most of the liquid away, keep a small amount as starter, top up with filtered or dechlorinated water, then a tablespoon of sugar and a tablespoon of fresh grated ginger daily, stirred, at cool room temperature. Three days and you should have ginger and yeast back with bubbles.

Flavour, not safety, and it is recoverable. What has happened is that one half of the culture has run away with it. Yeasts eat sugar and give you the fizz plus a little alcohol. Acetic acid bacteria then turn that alcohol into acetic acid, which is vinegar.

Underfed, left too long, warm, plenty of air: that is the exact set of conditions that hands the jar to the vinegar side. Your fortnight on a worktop is all four at once. The sugar ran out, the alcohol got converted, and the smell followed.