This comes up every now and then. If people want to randomly zap their brains that's their prerogative, but let's call a spade a spade. I sincerely doubt that anybody will ever improve their brain by shocking their scalp.

The underlying idea is sound; deep brain stimulation, which this is sort of analogous to, is a surprising if short-lived panacea to a wide range of conditions. Applied randomly it's as likely to exacerbate a negative effect as it is to treat one, but it is generally performed by a trained neural surgeon while the patient reports on how well it's working, and it doesn't last too long anyways.

TDCS is like deep brain stimulation in that it applies a current to your brain, but the effect borders on homeopathic. It's imprecise, the charge is (happily) too weak to bring about any real change in the brain from the scalp, and I doubt it's anything more than a placebo, best case.