(This pertains to my Lamentations of the Fall Lords setting based on the Myth video game series. More information about the Dwarf class in our campaign can be found HERE and HERE.)
If you were to take almost any piece of advanced dwarven technology (a dwarven explosive charge, for example) and transport it to a world which did not contain any member of the Myth world's dwarven race, it would not work. It would almost work, and one or two minor changes (say, a different ingredient in the explosive's chemical recipe) would usually be sufficient to restore functionality, but it would not actually work as-is.
Unbeknownst to them, the dwarven people are reality-warpers, who unconsciously and unwittingly exercise some minor control over the laws of physics in their environment. The Fey (elves, fairies, and their ilk) have similar unconscious reality-changing properties, and even though the Fey seem to be newcomers to the world of Myth, it is possible that they somehow share a common origin or ancestor with the dwarven species.
When a dwarf truly and fully believes beyond all doubt that something that they or another dwarf crafted is going to work, it generally does, provided it is close enough to something that would work otherwise. Determining what counts as close enough would require much study. Since dwarves are culturally inclined to have a great deal of faith and confidence in their work, they tend to build things that function even if they "shouldn't."
Basically, they're like the Orks from Warhammer 40,000.
When a dwarven inventor gets incredibly close to having a breakthrough, instead of putting in that final bit of work needed to have their "Eureka!" moment, they just go ahead and have that moment because the local fabric of reality changes itself to make things function as the inventor expects. This goes for architects and engineers, as well; many dwarf-built structures could not stand if other beings tried to craft them on other worlds. Dwarves cannot control this ability and do not even know it exists.
This is a very weak, low-level effect that does not seem to apply equally in all cases. Almost no one even suspects that dwarves have this inherent power, since the tech-level of the Myth world is rather low outside of the inventions of dwarven scientists and human mages, the latter of which almost exclusively creates technology which explicitly makes use of magic. Few understand the laws of physics, chemistry, etc. enough to consider the possibility that something odd is going on with the supposedly non-magical technology they encounter. Even if they did, what evidence would they have? Dwarven technology works in a repeatable, verifiable way in the world of Myth, so who's to say that something is "wrong?"
It doesn't help that spells like Dispel Magic and Anti-Magic Shell do not disable dwarven technology unless they are cast by someone of at least Level 20. The reality-warping effect is only weak in the sense that forces like gravity are weak.
In theory, dwarven reality-warping could affect a much greater variety of things than just bombs, buildings, and the like. However, the Dwarven Kingdom is still recovering from many social/cultural setbacks resulting from the various Dark Ages as well as their own unique struggles throughout history (as depicted in Hammers of the God). In dwarven society, scientific thinking may be relatively uninhibited, but cultural thinking is still fairly rigid. Such rigidity may strengthen certain beliefs, but it also leads to a lack of imagination in many aspects of thought.
When the dwarves first arrived by whatever means in the world of Myth, deep in prerecorded history, their powers may have reacted to their environment in such a way as to shape their physiology. If they had ended up living in forests instead of mountains and caves, they might have become willowy creatures with a supernatural aptitude for woodworking and herbal medicine.
If the dwarves were ever to discover their true potential, who knows what they would accomplish? Perhaps they would be a race of gods.
New house rule: As a character of the Dwarf class levels up, their belief in the success of their explosive weaponry becomes stronger. When a Dwarf character of at least Level 4 attacks with a dwarven explosive, any targets make their saving throws at a penalty of -1. This becomes -2 at Level 8, -3 at Level 12, -4 at Level 16, -5 at Level 20, -6 at Level 24, and -7 at Level 28.