Im not sure where the OP got the impression that Temp HP from different sources stack, or where the quote above got the impression that this is how things worked. This is the text from Combat section of PHB (Page 294)
You've misunderstood me. I know that different sources do not stack. I was wondering what the definition of "sources" was. I said as much in the opening of the post:
According to the PHB, you don't add up all your Temp HPs from all sources...but what counts as a separate source?
(emphasis mine)
This matters because if "sources" means a single
event, an item like the gloves or something like the Pact boon can only provide you with a tiny amount, repeatedly. If, OTOH, "source" would be the item or Pact Boon
itself, then it can provide a bunch of THPs.
For example: if a PC wearing the gauntlets triggers their effect, he gets 2 THP. If they work the first way- if each triggering
event is the "source"- the wearer will not be able to trigger the gauntlets' effect and gain THP until he loses at least 1 of the 2 he gained the first time. Essentially, the gloves will only provide 2 THP total at any time. At best, he will keep getting a "reset" to 2 THP.
If, OTOH, it works the other way- if the
gauntlets are the "source"- he'll get the +2 for the first triggering, +2 the next, etc., actually increasing his THP total.