The absolutely cheapest way is to step out for trip to nearest bug market, where used second hand mobile phone chargers cost under 1 USD. If it case is disturbing, just crush it. Last time I bought 100 pieces for 10 bucks and everyone was good.
Another very nice system between zero and 30W is TNY265...268...27x in the circuitry like many at danyk.cz
Only problem there, is lazyness to wind a ferrite core transformer.

 

hi,
There are lots of inline mains to 5Vdc available.
https://www.google.com/search?q=inline+mains+5+volt+psu&ie=utf-8&oe=utf-8&client=firefox-b

Hi,

Would be nice with a 120vac power connector instead of screw terminals.

 

Would be nice with a 120vac power connector instead of screw terminals.

Just mount it in an enclosure and add a male power receptacle:


There are a lot of open frame power supply options:


We're shooting in the dark because the OP clearly has something in mind, which he isn't sharing, and has found something to dislike about everything that has been suggested.

 

Hi,

Not a bad idea really, but it may be hard to somehow get the wall wart mounted properly and i think it would look more like a hack than anything else. Something i would do, except in a production environment where the final project has to look professional.

But that idea leads to anther idea, to use an approved computer power supply. These things are meant to be mounted inside another box and so would look like a professional product once completed. These things have a cord connector for a regular computer power cord, so i think it would work pretty nice. That is, unless the AC power is needed for another part of the circuit too which would then require either another AC input or mod of the computer power supply.
Computer power supplies come pretty small, or at least they used to, but just what the smallest is i dont know and hopefully it would not be too big for his project.

I have done just exactly that!! We took the very same power supply, purchased from Digikey, with an IEC power inlet connection, and mounted it inside the case of our instrument. The customer was completely happy with that and we were saved on a production run of 24 systems . And we never had a single failure of those supplies in 15 years. That supply was a regulated switcher, 120 volts in and 12 volts at 1.2 amps out. So while DigiKey is not the cheapest they do sell good stuff.

 

Just mount it in an enclosure and add a male power receptacle:
View attachment 159889

There are a lot of open frame power supply options:
View attachment 159890

We're shooting in the dark because the OP clearly has something in mind, which he isn't sharing, and has found something to dislike about everything that has been suggested.

Hi,

That's a good idea too. However, i was talking about a ready made unit with power plug/jack already on it like a regular computer power supply (see MisterBill2's reply) as i was hoping that would help meet regulations a lot easier. A power supply that is already fully contained like a PC power supply must already have passed the required government mandated electrical standards which could make it substantially cheaper for small companies.

 

What happens, especially with small production runs in small companies, is that the sales person has neglected to get one small detail that should have been defined clear. Things like the specific power inlet connection. That happened to me, and the solution that I suggested was the answer. In addition, while the open frame power supply can be a very high quality unit, the required certification can't be available for it because it is not certified to be "stupid proof." That is not the actual name of the spec, but what it means is that the supply must not have any points that a fool could deliberately touch that might connect to any part of the circuit. Thus only a supply intended for external service is applicable. I was very fortunate in that our product had room inside the enclosure to mount the table-top supply that we had already purchased. So the production run of 25 units was saved.