Its just my opinion, but I would (never) buy a Pwr Supply (used).. I've had stuff kill my stuff when I got it and found the internal leads shorted or fused.
Mouser and Digikey carry a full line of wall adapters and you can filter by many variables.. its dizzyingly flexible.
That said.. I do buy power supplies off eBay
(of a particular brand) and now test them with a multimeter for voltage before using them.
As for brand.. I only trust PhiPhong now. They have been making wall adapters for years and obviously are first to market with new technologies far in advanced of other companies. Many companies for many years (20+) have sourced them.
[see: PhiPhong photo below]
Sometimes I think the cost doesn't matter or stray.. but I always come back to that brand.. its safe, stable, and they make every kind you can imagine.
Imagine my surprise when I got an ATI TV Wonder USB2.0n and it had an offbrand, unknown manufacturer power supply.. which eventually I found was underpowered and just did not work!
I got another ATI TV Wonder USB2.0n and it came with a PhiPhong power supply.
Later I discovered in the ATI HD Wonder 650 users manual the offset and gray background [WARNING: Make sure you use the PhiPhong XYZ... power supply supplied with your device!] They were deadly serious about quality and stability.
Another nice (benefit) to PhiPhong is their adapters consistently are hard shelled, tough and are the smallest possible in size to do the job. That hard shell will dissipate a lot of heat if it needs to without melting the adapter. And they have a really nice mechanism for switchable modules for International adapter pins.. its a soft button press to remove the pins that come on it, and slide in a new set of pins. Since most are universal switch supplies they tend to run the gamut of possible input voltages and produce the same output voltage required.
[see: PhiPhong2 photo below]
They have an [excellent
] documentation label, with extreme detail on inputs, outputs, capacity, polarity of the plug in universal symbols.. no one else does this.. they are outstanding with these labels.
The power cables are re-enforced at their attachment points to the adapter and the cable connector.
[.. a littl background story.. years ago] when I first ran across my"first" PhiPhong I thought it unnecessarily complex and "adaptable" it just came with so many options and was a tad heavy, wide and .. well I didn't know what I was expecting but.. since I didn't know any better.. I looked for wall adapters (mains adapters) that suited my creature comforts.. slim, right angled.. left room for other plugs or wall adapters in a power strip.. gosh.. was I stupid..
Eventually over time I've learned every single "feature" or extra PhiPhong built into their adapters had a purpose.. and was eventually very useful in a crisis situation.
They are competitive in price, but Not the cheapest.. and thats a difficult balancing act to do.. they (might) make some bad apples.. and I'll probably regret recommending them someday.. but they have been a really good training ground for me.
Now all of (that) said.. always check the voltage of your adapter.. and Especially the (Polarity) of your DC plug.. reversing it by accident [may] kill your device.. or it [may] survive.. but its a darn sure way to Whallop it good.. and possibly damage it.. check.. check.. check.. protect your gear, that's your job.. not theirs.
.. an lastly, the PhiPhongs look like black turtles.. I've come to respect they aren't the prettiest things in the world and need their space.. they don't play well with other adapters near by or leave space for other types of plugs around them.. but now its an ugly.. I've come to accept and even (like).. other wall critters just scare me.