Direct current?

Since its a power supply, the current direction is not an issue…it will flow from your wall outlet, through a transformer and then through the jack you plug into your device. What is most important is matching the type of power (AC as in house power versus DC as in an automobile’s power) as well as voltage and the amount of current. I don’t have a laptop so I can help you with that type of device. But if the device and supply don’t match you do risk harm to either or both, although they may have some sort of built-in protection (e.g. a fuse or circuit breaker). Good luck!

I know the volts and the amperage frem the battery, so it’s probably safe to assume that the PSU should deliver the same amount, and I know that it’s DC. The problem is what happens if I turn the current the wrong way, ie send + to the – terminal. The universal PSU I have can change the polarity, and I don’t know what’s + and – on the jack in the laptop.

If both devices are not marked with an indication whether they are center pin positive or negative, refer to the instruction manual or specifications, but don’t guess. The indication is a symbol of a center pin with a plus sign on one side and a negative sign on the other side. The symbols must match,

That’s what I feared. Thanks a lot!