I picked up a 9V switching DC adapter from SparkFun a while back, but I've been hesitant to use it because it doesn't have any of the usual "safety" approvals that you normally see on power adapters (UL listed, CSA approved, etc.)

Is this just unfounded paranoia? Are there safety issues to think about when using a DC power adapter for a project that will run 24/7?

  • \$\begingroup\$ In my particular case, we're talking about low-current devices/microcontrollers. I am well within the limits of the DC adapter. \$\endgroup\$ Jul 25, 2010 at 22:53
  • \$\begingroup\$ Fine. You bought a 9V switching DC adapter. But what does "DC adapter" mean? Could someone please edit the question and clarify? \$\endgroup\$ Jun 19, 2015 at 16:38

8 Answers 8


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 — 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.

  • 1
    \$\begingroup\$ Safety approvals may cost a lot, but they usually get done by companies that are selling a lot. The savings of manufacturing in bulk usually is pretty close to matching the cost of getting safety approval. With this said, you should be able to buy a certified adapter for about the same cost of a non-certified. \$\endgroup\$
    – Kellenjb
    Jul 26, 2010 at 12:43
  • \$\begingroup\$ SparkFun is a reseller. Unless they actually make the adapter themselves, they won't be the one applying for UL. Like Kallenjb says, it's cheap enough for manufacturers selling in bulk. Personally, I would never use unlisted adapters even if the application well within it's spec. In the off chance, you get a bad part, you can't predict how it will fail. \$\endgroup\$
    – Vineeth
    Jul 26, 2010 at 17:07
  • \$\begingroup\$ That's what I suspected-- I essentially have an unknown black box. Even if it is well engineered, I'll spend the $7 for a new one with the safety approval. At least I know now to check for approvals along with all the other specs on the supply. \$\endgroup\$ Jul 26, 2010 at 22:37

UL listed means that even if the device shorts, you will not get electrocuted when you touch it. Given that it's not expensive to get an UL certified DC adapter (less then $10), why take the chance?

  • \$\begingroup\$ Any tips on where to find a reasonably priced, quality adapter? ie. a switched mode power supply with reliable voltage and current ratings? If I could find one on Amazon.com, I wouldn't have ordered from SparkFun. \$\endgroup\$ Jul 26, 2010 at 2:56
  • 2
    \$\begingroup\$ I get all of my wall warts from CUI through Digikey. Their products work well, their customer support is excellent, and their prices are decent. They're also UL certified. I've found that their switching regulated power supplies (link bit.ly/aKc9kZex) do really give a +/-2% regulation even at no load and continue to do so all the way to their maximum current, after which they taper off without damaging themselves. \$\endgroup\$ Jul 26, 2010 at 14:44
  • \$\begingroup\$ I would be surprised if you couldn't get one in any local electronics store. On Amazon - amazon.com/15-Watt-9V-1-7A-Power-Adapter/dp/B002QHIVGK/… . \$\endgroup\$
    – Vineeth
    Jul 26, 2010 at 17:25
  • 1
    \$\begingroup\$ -1, UL listed means so much more than being double insulated. \$\endgroup\$
    – Nick T
    Oct 3, 2010 at 4:01
  • 1
    \$\begingroup\$ +1 @NickT He didn't say it didn't. He just added another positive point to the list. The answer is useful if not complete. So -1 is improper. \$\endgroup\$
    – Russell McMahon
    Dec 23, 2014 at 21:04

The problem is with certification marks, like anything else - they can be faked. Go to globalsources.com, find a cheap manufacturer, they will most likely say "email us the artwork and we'll add it to the transformer!".

In defence of Sparkfun, I wouldn't think they would risk their reputation over such a thing. But it couldn't hurt to ask them about it.

Personally I spend a lot more and get the certified ones with the half-insulated pins as specified by the Australian standards (being in Australia). As after this experience, I don't like to take any chances.


Bear in mind also that there are other companies doing safety approvals for North America these days. Just because there isn't a UL or CSA mark doesn't mean that there are no approvals whatsoever on the product. (ETL and MET are examples).

If there aren't any recognizable marks at all on the product, well, your mileage may vary.


Getting a UL stamp means you meet a number of safety tests for your equipment. In the US a UL stamp is only 'required' on some electrical equipment in some markets, generally items running on main power but there are some exceptions and only when its being sold or placed in some public areas, for instance a school. Even then a UL stamp is completely optional, however a local inspector may not allow a non-UL device in a building. Needing to be UL listed is completely a political issue not a technical one.

The documents that cover a UL listing are long and cover many issues from shock prevention, reducing the chance of a fire, RF emissions, etc.

As one example you could use a UL listed power supply to power a low voltage device, something like a laptop brick, but if you place that brick within an enclosure it is no longer UL compliant.

UL listing is really a hoop you need to jump through for safety compliance for a product your selling as defined by the market your selling that product to. I wouldn't try to put a non UL listed part in something like a school but for some applications its not needed.

Getting a UL stamp is expensive. The European version of the UL stamp is the CE stamp and it actually goes farther in various directions than a UL stamp does.

I wouldn't bother worrying or caring about a UL listing unless you know that your market or installation cares about that, the best way to determine this is to call you local electrical inspector and ask him about the issue at hand.


Using something like that might invalidate a household insurance policy. It would be a good idea to check the small print.


Any or all of UL CSA CE TUV ... certification is worthwhile IF GENUINE.
I have seen much Asian manufactured equipment which has had various certification marks attached with no prospect of there having been any related testing.

"Provenance matters" - ie you can usually be confident of certification marks when purchasing certified equipment via a competent & reputable large volume supplier with a good reputation and whose business is founded on professional customer service. Digikey qualifies for that. Sparkfun are trying hard and are good at what they do but I would not class them as qualifying. I'd still happily buy product from eg sparkfun, but I'd be discerning about things where safety mattered.
[I have no business interests in either supplier - I buy from Digikey occasionally. I don't think I've purchased from Sparkfun but would happily do so. I think enough of Digikey that if they sell a brand I'd consider it was probably an acceptable one to use, subject to specifications meeting need.]

Note that brands of popular products will often be faked in the general market and that buying through a reputable supplier is usually but not always protection against this.

If you are buying in any volume then pulling one apart to determine quality of construction is probably worthwhile.

  • A genuinely certified product should pass the "looks OK" test with ease.

  • Anything at all suspect almost certainly indicates a fake certification.

  • Mains voltage clearances should be acceptable, mechanical construction and component mounting reasonable.

  • Component ratings should be appropriate. Any electrolytics would ideally be 105C (not essential).

  • Generally (but not always) a product with fake certification reeks of fakeness internally - but externally MAY look as real as any.

A modern regulated power supply should meet voltage spec at rated maximum current without excessive heating. Simply loading one up with a (suitably rated) resistor to max load and letting it "set a while" is a good first check. Given any two or Power P, Volts V, Current I, then Resistance R for maximum load =

  • V^2/P

  • P/I^2

  • V/I

Suppliers on these sites are more likely than average to offer reputable product:


Ones I've not yet tried but which seem OK at a glance.


REALLY fun places.
YMWV !!!! [You mileage WILL vary]:



There are a variety of design, manufacturing and qualification requirements to meet UL, CSA and TUV. I would not use a line powered supply that does not meet these specifications.

I also tend to buy these supplies from name brand manufacturers and manufacturers that have ISO9000 approval even though it is difficult to know how/where a device was manufactured.

I would try to return the supply.


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