We got three SMPS from a local SMPS vendor for trial purpose. We never had any kind of problem with linear supplies but with SMPS the system shows weired behaviour.

My guess is that you got "I can make those" units.

My favorite statement about SMPS is "every engineer I know can design a SMPS, very few can design one that works".

An engineer here spent > 6 months designing, manufacturing and testting SMPS for our equipment and we still use "storebought" and have changed the one design of his that got produced to "storebought" for current production.

For less than a few Amps, I am, personally, a fan of the TI Power Trends PTxxxx series, they simply work, nothing else to say.

Since we use 60A SMPS as well, the cost there is significant and we have been through a lot of manufactureres and a local "I can make those". ALL the well known manufactureres have supplied well working (OK one had had a few thermal issues) supplies and the local "I can make those" could not achieve acceptable functionality. EMF radiation and EMI sensitivity was totally unacceptable. Oh, they worked beautifully in the lab.

I suggest you get a hold of your local TI distributor and get a set of PT modules for your app before you give up on SMPS.

Erik