How much can a power brick safely vary from what the device it's used with expects?
These bricks are constant voltage supplies, i.e. they're both spec'ed to deliver 19 V.

The 1.58 A and 3.42 A are specifications for the maximum current they can supply at that voltage – using less than the supply can offer must work.

Physically, a power supply can either define the voltage it offers, or the current it pushes through a load – never both, because for any load, one is a function of the other.