Електропостачання відновили вночі.

Because електропостачання is not the subject here — it is the object: the thing that was restored.

The verb відновили is past tense, 3rd person plural. Ukrainian often uses this plural form with an omitted, unspecified subject: basically they restored without saying who they are.

So the sentence structure is roughly:

[Someone / they] restored [the power supply] at night.

In English, this is often translated more naturally with a passive: The power supply was restored during the night.

This kind of subjectless 3rd-person-plural sentence is very common in Ukrainian, especially in news and reports.

It is in the accusative singular, because it is the direct object of відновили.

However, for many inanimate neuter nouns in Ukrainian, the accusative looks exactly the same as the nominative. So:

• електропостачання = nominative singular
• електропостачання = accusative singular

That is why it looks like the dictionary form.

Електропостачання literally means electric power supply or electricity supply.

It is a fairly formal and official-sounding word, common in:

• news reports
• utility announcements
• administrative language

In everyday speech, people often use:

• електрика = electricity
• світло = literally light, but very often used colloquially to mean power/electricity

So in daily conversation, you might hear things like:

• Електрику відновили.
• Світло дали.

But електропостачання відновили sounds more like a report or official update.

Відновили comes from the perfective verb відновити.

That means the sentence presents the action as completed: the power supply was restored successfully.

This is different from the imperfective verb відновлювати. For example:

• відновили = restored, completed
• відновлювали = were restoring / restored repeatedly / were in the process of restoring

So the sentence is not describing an ongoing process. It gives the result.

Вночі means at night, during the night, or sometimes overnight, depending on context.

In this sentence, it tells you when the restoration happened.

So the timing is something like:

• not in the evening
• not in the morning
• but during the night

In a news-style sentence like this, English often uses:

• during the night
• overnight

Вночі is commonly used as a single adverb meaning at night.
You can also see уночі — same meaning, just with у instead of в for smoother pronunciation in context.

So both are normal:

• вночі
• уночі

For a learner, it is easiest to remember вночі / уночі as fixed adverbial forms meaning at night.

Yes. Ukrainian word order is quite flexible, and changing it usually changes emphasis, not the core meaning.

For example:

• Електропостачання відновили вночі.
  Neutral, report-like. Focus starts with the power supply.

• Вночі відновили електропостачання.
  Puts more emphasis on when it happened.

• Електропостачання вночі відновили.
  Possible, but more marked; it can sound contrastive or emphatic.

The original version sounds very natural in official updates and news reports.

Yes. A more explicitly passive version would be:

Електропостачання було відновлено вночі.

This is also correct, but it sounds more formal, bureaucratic, or written.

The original sentence, Електропостачання відновили вночі, is often more natural in standard reporting style. Ukrainian frequently prefers this active-looking structure with an unspecified they, where English might prefer a passive.

Yes, but the style changes.

• електропостачання = formal, technical, official
• електрика = neutral everyday word for electricity
• світло = very common colloquial way to mean power/electricity in context

So these are all possible, but not identical in tone:

• Електропостачання відновили вночі.
  Official/reporting style

• Електрику відновили вночі.
  More everyday, still clear

• Світло відновили вночі.
  Understandable, but less technical

Very often in casual speech, people might say something even more idiomatic, such as:

• Світло дали вночі.

That sounds much more conversational than the original sentence.