Doing a bit of digging we can see this:
Listed: https://wiki.puri.sm/hw/L13/v3#ram-removal
It appears to say Kingston with some numbers/letters
Typing the codes into my search engine I found this: https://www.amazon.com/Kingston-KVR26N19D8-16-ValueRAM-Computer/dp/B0721M46Y2
I am unware of any changes Purism makes to its RAM.
Although, I would like to get a confirmation on this.