Is it safe to use a DC power adapter that isn't UL Listed or CSA certified?
Safety approvals cost (a LOT of) money. You won't find anything from sites such as SparkFun displaying these logos. It's not because they're unsafe &mdash; it's because it's prohibitively expensive to get the testing done to prove they're safe.

If you are buying things from sites such as SparkFun, etc. it is also assumed that you are experienced enough to work safely. Personally, I have zero problem using unlisted equipment, but then again I am in the business of designing this kind of equipment and have a pretty good "feel" for circuit safety and design capabilities based on observing the parts and quality of manufacture. I've seen some pretty sketchy stuff in my time, but I haven't gotten the screaming heebie-jeebies from anything from sites like that.

That being said: Use it at your own risk. If something doesn't feel right to you, don't use it.