Nothing should happen, because it won't be recognized as a Genuine charger and thus won't charge. Just as with printer cartridges, the 3rd party aftermarket suppliers have to connect a special circuit, here to the sense pin, which doesn't always work as it's undocumented and thus reverse engineered. Even if it works it will only do so with a limited number of laptop models.
Chargers and lithium batteries can burn your house down if the smallest things go wrong, and since even the genuine ones from big name brands have been the subject of many fires and recalls, why take that risk? At least those cheap USB chargers
will only kill you. Get a used, genuine charger after checking if it's been recalled.