The general rule is that the highest value of each specified type is overwriting the lesser value.
If the effect of both items are called the same name, then it usually means that their effects won't be stacking.
The +16HP/10s is tied to the Strength of Purpose effect and should appears among the list of buff on you.
As such, if you want to see if certain buff effect stack, you can check the full list of buff/debuffs on your character by examining yourself.
(Select yourself and press the gear icon on the selection preview/window and select "Examine".)
Any named buff that stack would appears multiple times in that list of buff/debuff.