A empresa restabeleceu a eletricidade, assim como prometeu.

Restabeleceu is the 3rd person singular of the preterite (the simple past) of restabelecer.

• restabelecer = to re-establish / restore
• ele/ela/você restabeleceu = he/she/it/you restored

In this sentence, it describes a completed action in the past: the company restored the electricity.

Portuguese normally uses the noun itself much more often than English does, especially when introducing the subject clearly.

So instead of starting with It restored the electricity, Portuguese often says:

• A empresa restabeleceu... = The company restored...

Also, Portuguese often drops subject pronouns when the verb form already makes the subject clear. In the second clause, prometeu has no written subject, but we understand it as a empresa.

Because Portuguese is a pro-drop language, meaning subject pronouns are often omitted when they are understood from context.

So:

• assim como prometeu
  literally looks like just as promised but really means
  just as it promised

The subject of prometeu is understood to be the same as the earlier subject, a empresa.

Here, assim como means just as or as, in the sense of in the way that.

So:

• A empresa restabeleceu a eletricidade, assim como prometeu. = The company restored the electricity, just as it promised.

Be careful: assim como can also mean as well as in other contexts. For example:

• A empresa, assim como os técnicos, participou na reunião. = The company, as well as the technicians, took part in the meeting.

In your sentence, because it is followed by prometeu, the meaning is just as.

Yes. Como prometeu is also natural and would usually mean the same thing here:

• A empresa restabeleceu a eletricidade, como prometeu.

Adding assim makes it a little more explicitly just as / exactly as. Both are possible, but assim como prometeu sounds slightly more formal or carefully structured.

The comma separates the main statement from the added comment:

• A empresa restabeleceu a eletricidade
• assim como prometeu

That second part works like a parenthetical comment meaning just as it had promised.

In writing, the comma is very natural here. It helps show that the second clause is not introducing a new event, but commenting on the first one.

Portuguese uses definite articles more often than English.

So where English might say:

• restored electricity

Portuguese normally says:

• restabeleceu a eletricidade

This is especially common with general, concrete things like services, body parts, abstract nouns, and many everyday references.

In this sentence, a eletricidade means the electricity supply/power.

Not exactly, though in everyday speech they can overlap.

• eletricidade = electricity
• luz = light, but also often electric power in daily usage

In Portugal, people very often say things like:

• Foi abaixo a luz. = The power went out.
• Já voltou a luz. = The power is back.

But in a more formal or technical sentence, eletricidade is a very good choice:

• A empresa restabeleceu a eletricidade.

So eletricidade sounds more formal/official; luz is often more colloquial in this context.

Because Portuguese often uses the preterite for both actions when the sequence is clear from context.

• restabeleceu = restored
• prometeu = promised

Even though the promise happened earlier in real time, Portuguese does not always need a separate had promised form.

So this sentence naturally means:

• The company restored the electricity, just as it promised.

If you wanted to make the earlier action more explicit, you could say:

• A empresa restabeleceu a eletricidade, assim como tinha prometido. = The company restored the electricity, just as it had promised.

That version adds extra emphasis on the promise being earlier.

Restabelecer means to re-establish, to restore, or to bring back to normal.

In the context of electricity, it means restoring supply after an interruption.

• restabelecer a eletricidade = to restore the electricity / power supply

Restaurar can also mean restore, but it is often used in slightly different contexts, such as:

• restoring a building
• restoring a file
• restoring something to a previous condition

For utilities and services, restabelecer is especially common:

• restabelecer a ligação
• restabelecer o serviço
• restabelecer a eletricidade

Yes, it fits European Portuguese perfectly.

A useful spelling note: after the orthographic agreement, the standard spelling is eletricidade. You may still sometimes see the older spelling electricidade, especially in older texts or among people who prefer pre-reform spelling, but eletricidade is the modern standard.

Also, the overall phrasing sounds quite natural for formal or semi-formal European Portuguese.

The original sentence is correct and natural, especially in a formal or written register. In everyday speech, people might also say:

• A empresa restabeleceu a luz, como prometeu.
• A empresa voltou a pôr a eletricidade, como tinha prometido.
• A eletricidade foi restabelecida, como a empresa tinha prometido.

In Portugal, a very common everyday version would often involve luz rather than eletricidade, depending on context.

In European Portuguese, restabeleceu is pronounced approximately like:

• resh-tuh-buh-luh-SEU

A few pronunciation points:

• s before t often sounds like sh
• unstressed vowels are often reduced in European Portuguese
• the stress is on the final syllable: -ceu

And eletricidade is approximately:

• i-leh-tree-see-DAHD

The exact sound will vary a bit by region, but the important thing is that European Portuguese usually reduces many unstressed vowels much more than Brazilian Portuguese does.