Advice on Buying a Regulated Switching Power Supply?

I have two questions:

  • By how much (if any) do I want the rated current of the power supply to exceed the current I expect to be drawing (2-3 A)?

  • I'm attracted by the low prices of the units on ebay, especially seeing as I don't need more than 9 V, but what is the likelihood of such a cheap unit blowing up, catching fire, etc., even with everything wired correctly, including ground? (On that note, if you can recommend a reliable supplier of regulated switching power supplies, I'd appreciate it.)

Thanks.

I use these wallwarts regularly.
http://www.dipmicro.com/store/index.php?act=viewCat&catId=518

5V, 4A:
http://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520%20PS/

I often design/build to not have onboard regulation, just a 10uF cap where 5V from the regulator comes in, and 0.1uF cap on Vcc pin(s) of each IC used.

10% should be plenty, unless you are driving motors. Then you need to account for the motor stall current also.
Most switching regulators will shut down when the output is exceeded, or shorted out even, without damaging anything, and recover when the short is removed.

Thanks. I hadn’t given much thought to wall warts before, but they certainly seem like a better (and safer) idea than the type of power supply I was considering (http://www.ebay.com/itm/Aluminum-Universal-Regulated-Switching-DC9V-3-8A-35W-Power-Supply-Converter-/370929625866?pt=LH_DefaultDomain_0&hash=item565d20eb0a).

Also, since I only need to power dc and servo motors directly (no microcontrollers) with this power supply, would I need to be concerned about inserting additional capacitors like you mentioned? (I assume you use them only to further smooth out the dc current?) Thanks again.

I wouldn't think you'd need additional caps for motors, no.