The 18.5V one would probably work.
However (assuming that it's the same type of plug at the laptop end of the cable in the first place) you need to check that the tip polarity is the same way round. (e.g. I've just looked at the charger unit for my netbook. The markings on it show that the inner part of the tip is positive and the outer part negative). If it was the wrong way round and the laptop's manufacturer had fitted a protection diode, it simply wouldn't provide any power to the laptop. If it was the wrong way round and the laptop's manufacturer had saved a penny or two by omitting that diode you'd ruin the laptop.
Further, and very importantly(!), you'd need to check that the current rating of the 18.5V charger was at least as high as that of the 19V one (it wouldn't matter if it was higher). If the 18.5V charger was asked to provide more current that it was intended to do it would overheat and burn out.