As sold

I bought this for a custom made LED lamp and so far have had no problems with it, I like that it's low profile and the only thing that I don't like is that the 120v cable is a bit short.

I'd like to address a few things I've seen in other reviews, as there are a few things I don't fully agree with.

1. It doesn't come with a connector on the 12V side:
As you can see from the photo, the 12V cable ends in bare wires (tinned) coloured Red & Black (for + & - respectively) additionally the description makes no mention of any connector so I'm not sure why people are surprised by this. Given that there are thousands of connector types on the market which are all "Standard" to some degree, it's hard to make something that will work with everything. As it stands, the easiest way is to simply leave the end bare and either solder (which is what the MFR intended) or attach the connector of your choice.
TL;DR: If you need one with a connector, buy a power supply/driver/transformer that has that one.

2. No Manual:
I can answer this in a single sentence: Red wire goes to the positive input on the LED strip (etc), Black wire goes to the Negative, plug the mains cable into the wall. If that isn't enough instructions then it's not an issue with the transformer, it'll be something about whatever it is you're powering.

3. Failures:
Hey, things break. Unfortunately as people are much more likely to post a negative review than a positive one, it's really hard to say what the actual failure rate is on this. That said, these things are cheap. Caveat emptor.

4. Loading:
This is a 12V 30W transformer, so the current output is 2.5A, while you can go past this it will shorten the life of the transformer. On the other hand, you don't have to use the full overhead, this transformer will just as well putting out 1A or less.

All in all, if you buy this you should either know what you're doing with it, or be prepared to learn.

I bought 2 power supplies (15 watt) 6 years ago: both just died within a couple weeks of eachother. For the price I think 6 years is a reasonable life space. Ensure they're installed in a location where it is accessible to be replaced!

This power supply works as advertised, I was able to power a long strip of LEDs with minimal problems. When I had the unit under load, I noticed that it would get very warm, almost too hot to touch depending on your heat tolerance. I did have the unit at about 85% load, so I expected some heat, but not very much since it gets only intermittent use at about 15-20 minutes per use. It does have an aluminum case which I suspect is tied to the regulators inside so as to use it as a heatsink, a common practice on low-end power supplies. I haven't tested its water resistance, but the aluminum case does not have any apparent seams down the length and the ends appear to be properly sealed off. This unit still works fine for powering LEDs, (or anything else) just be aware that due to the design, you'll want to make sure that it is placed where it can get a reasonable airflow and of course don't have it touching anything that is more flammable than the norm or touching anything that could melt, even a few inches away would probably be sufficient to prevent problems. All in all a decent power supply for the low price point.

Nice little power supply. The output measures at 12.07 with no load. But for my use it can make a high pitch humming/buzzing noise if the output is limited below 12 volts. I use this with a 12v dimmer (item #B003L4KKF2) to power some LED ribbons, and when I turn the knob to anything but off or full on the supply makes that noise. I'm not sure if it's the dimmer or the supply's fault. The dimmer is PWM (pulse-width modulation), so it switches the voltage on and off at a high frequency, which is probably why the power supply buzzes when the voltage is limited. I'm not sure if this will be annoying in the long run as this supply will be powering some LED strips that will most likely be dimmed. Maybe I'll just have to find a new 12v dimmer (item #B004AGZSQG) that doesn't appear to be PWM.

UPDATE: I have found and fixed the cause of the humming/buzzing. It was the dimmer's fault. By putting 2 16v 1000uf capacitors across the input of the dimmer, I was able to reduce the buzzing by 99%. I'm sure the correct value of capacitor will fix it 100%.