Adding RAM to Inspiron 3650

I have an Inspiron 3650, with 8 GB of RAM, and would like to add another 8 GB. I've looked online and have seen posts saying that it's not a good idea to add RAM from a different manufacturer, because it could cause problems.

Yesterday, I downloaded CPU-Z and according to the SPD tab of  this program, I have 8 GB of RAM, manufactured by SK Hiynix, DDR3L, PC3-12800 (800 MHZ), part number HMT41GU6FR8A-PB.

The specs in my manual say my RAM is 1600 MHz. Should I trust what CPU-Z says and buy this RAM or is this wrong?

If this isn't right, what would work in my Inspiron 3650?

Would it be better to just buy a 16 GB module, and discard the 8 GB module that's already in there?