Vitamin C as ascorbic acid is obviously acidifying. The thing is how much is taken and how pH balanced is the person taking it.
A lot of the buffered Vit C is calcium ascorbate.
You may find other kind of ascorbate like sodium ascorbate.
There is an expensive brand that combine several kind of ascorbates (sodium/calcium/magnesium/potassium ascorbates).
You can also make your own sodium ascorbate by mixing in a glass of water some ascorbic acid powder with baking soda. I don't know the exact formulation, but I know a few posts in curezone describe the very simple protocol. Just use the search engine in CZ or google, you should find it quickly.