How to differentiate original and fake Apple 5W USB EU power adapter A1400 / MD813ZM/A? I did receive a European 5 watt USB charger model A1400 that claims to be from Apple. The charger even claims to be designed by Apple in California and made in China. Possibly by "Salcomp".

The "made in China" part, is most likely a valid claim.

But how can I find out whether this USB charger is a counterfeit or a genuine Apple product?

I do own a genuine A1300 that came with an iPhone that was bought in an Apple store in Oberhausen. The 230V pins two USB chargers are shown in the photograph below:



Here is a photograph of the serial imprint inside the USB connector from both an "A1400" and an original A1300:


And here the imprint the "Certification Label" of a possible counterfeit A1400:


PS I am aware of the A1300 to A1400 Exchange program and don't use the A1300 any longer for charging purposes.
I got here by having the same problem as you and googling it. :)

I got my 5W EU charger (i'm sure now that it's fake) from a local seller, because my brand new SE was for UK market, so i had their three pin charger in the box. The one that i bought had a problem i noticed shortly. When i tried to charge my SE with it, touch sensitivity would go crazy. I compared it with my girls charger (she got it with her 6S in the box, for French market) and it was working flawlessly. There are couple differences between those two. Metal pins are different, fake one is lighter and you can bend the plastic housing a little when you press it harder.
They even made serial number readable, but pins and weight betrayed them.
I will post pics tomorrow when there is daylight so i can make better macros.