Question about memory compatibility and using different memory sticks

[Smoshi]

With Black Friday here I'm looking to upgrade my ram. I'm currently using 8GB DDR4 (http://eu.crucial.com/eur/en/bls2c4g4d240fsb). I want to upgrade to around 16GB. I've seen a couple sales so far that has really good deals on 16GB DDR4 but the problem is, can I use it with the current ram I'm using?

Here's my motherboard; https://www.asus.com/us/Motherboards/PRIME-Z370-A/

I have 4 slots total for memory. If the memory I get has the same specs as my current memory, do you think it would be compatible? Or should I just replace the 8GB with 16GB and sell the 8GB.

Thank you.

Just for reference here are the two sales I was looking at (one is sold out now but I'm sure others will pop up soon that is similar)

https://www.amazon.com/dp/B01EI5YZSA/ref=ice_ac_b_dpb_twi_col_3?s=electronics&ie=UTF8&qid=1541941858&sr=1-3&keywords=8gb+ddr4

https://www.newegg.com/Product/Product.aspx?Item=N82E16820012085

 

[jojesa]

I suggest you sell the 8GB and get a 16GB RAM kit to avoid issues.

It is not recommended to mix RAM modules that were not tested to work together, since it is hard to predict the outcome.
Even though half of the time it might just work fine, mixing and matching stick that may have different speed, CAS latency, timings,voltage, etc could cause a motherboard to refuse to work
Even when they appear to be similar, the IC chips might come from different manufactures.
To be sure that RAM will work together you will have to buy RAM kits.
That's why manufacturers and vendors won't provide support for that configuration.