...one of those long strips of hard plastic, with a thick cord, into which you can put several electric plugs? (Not a surge protector--you just plug things into it.)

I was doing one of those hidden-picture puzzles, and searched for ages for something listed as a "power bar". I was looking for snack food, and it turned out to be one of these things, that I call a power strip!

Adapter? (Not sure of the spelling)
Spike buster?

I would normally call it a power board?

I call it a power strip

I call it a power strip

Me, too.

Good for you that make a distinction between a contact device for one and one for many contacts.
We keep it quite simple and call them, all for one, one for all:
contact box. ( just like the single one that sits in walls )
BTW, how do call the one or twins in the wall in English?

I don't think I've ever seen a single one. In these parts they're called (somewhat schizophrenically) outlets orreceptacles, sometimes prefaced by electrical.

Over here they tend to be referred to as "extension leads" - sometimes, "muti-plug extension leads," to differentiate from the single socket extension leads.

"how do call the one or twins in the wall in English?"

In my house we'd normally use 'double adapter'.

In this part of the world they are "plugs" or "outlets".
Sometimes "wall socket".

We call em Multi Plugs

Plug is a good word. Good enough to use for all devices I don't know the word of. Just will call them plugs.

The plug is at the end of the cord coming out of the lamp or whatever. The thing it plugs into is a socket.

Thank you Faldage, I'm sure Jackie is aware of this. I went on a trip after sock and socket and stumbled upon an blood chilling issue:

sockdolager
1830, "a decisive blow," fanciful formation from sock (v.) "hit hard;" also said to be a variant of doxology, on a notion of "finality." The meaning "something exceptional" is attested from 1838. Sockdologising was nearly the last word President Abraham Lincoln heard. During the performance of Tom Taylor's "Our American Cousin," assassin John Wilkes Booth (who knew the play well) waited for the line "Well, I guess I know enough to turn you inside out, you sockdologising old man-trap," and as the audience laughed, Booth fired the fatal shot.

Can you confirm this as a true story or is it a legend ?

it certainly is widely quoted.

Me also. So do all the techs I know.