Speaking to the memory first. There are NEVER any guarantees when adding memory. It's ALWAYS best to buy multiple modules in a matched set. So, if you want 16GB, it's always best to go with 2 x8GB in a matched set. ANY time you buy different, or even exactly the same model number, but not in a matched set, you stand a good chance of them being incompatible and not wanting to play nice together. This has become an increasingly worse scenario as memory manufacturers have increasingly taken to reusing model numbers on modules that have had drastic changes made to the configuration of the modules as well as the memory chips used on the modules.
Even buying two identical part numbers, at different times, is no guarantee they will work together at all, or most especially, in dual channel operation. See this thread for more examples on that so that you understand the underlying problem with this. Whether it is an AMD or Intel system makes NO difference when it comes to potential problems with memory compatibility. This has always been a potential issue and it has gotten worse in the last two or three years due to the lack of consistency in manufacturers using the same configuration and materials on different production runs even when part numbers are the same.
http://www.tomshardware.com/answers/id-3610013/amd-ram-compatibility.html#20562100
As for the power supply. ATNG is not known for good quality or reliable power supplies. Of course they CAN make some good models, and there are a few models they've made through the years that show at least some minimal improvements to their platforms, but in general they are not a go to OEM for power supply platforms or units. I would not trust it much and would be highly inclined to recommend an upgrade to a solid, high quality unit.
To tell you anything SPECIFIC, I would need to know more than just the brand and wattage. There IS a model number somewhere on the unit. Look for the specifications decal on the power supply. It will be on one of the four sides or the back, and will look somewhat similar to this.