what can hcl do
The HCl in betaine-HCl, just means that HCl was used to neutralize the betaine. There is no HCl in betaine-HCl. Using betaine as a supplement will buffer your stomach and have no impact other than perhaps lowering acidity. Betaine is very bizarre stuff, so it may incidentally increase the production of stomach acid, but I know nothing about that. In most cases, stomach acidity is not the problem.