Can an Apple iPhone 8 charger at all charge a 12.9" iPad Pro 2nd Gen 2017 model totally out of juice after being unused for 1-2 months? Slow charge?
Yes. Plug it in and then turn off the iPad.
A &quot;normal&quot; phone charger only has a power output of 5W, so it will be very slow, but provided the iPad doesn't need that power in use, you can charge it. To ensure, that you actually have more power input than usage you will very likely need to turn off the iPad and even then it will charge very slowly.
If you have a MacBook depending on the  exact model it will charge much quicker. Especially the &quot;newer&quot; ones with USB-C can charge the iPad at a descent rate, because they can provice much more power through the port. However, I would also plug in the MacBook because the iPad has a quite big battery. Be aware that plugging your iPad into your MacBook causes inefficiencies, i.e. you'll be drawing more power in total compared to simply charge the iPad from the wall plug.