The power failure was the second nationwide since the beginning of the blockade, with the previous one occurring on Monday.
Grid operator UNE announced the outage on social media on Saturday, saying it would continue giving updates.
Cuba's Ministry of Energy and Mines said a total disconnection of the National Electric System took place and protocols to restore electricity service across the country were being implemented.
Last week's blackout lasted more than 29 hours, amid a US move to choke off the island's fuel supply.
In addition to cutting off oil sales to Cuba, US President Donald Trump has escalated his rhetoric against the Communist-run island, saying he could do anything he wanted with the country.
A US State Department official blamed the Cuban government for the grid collapse, calling blackouts a "symptom of the failing regime's incompetence".
Cuban President Miguel Diaz-Canel fired back at Washington, criticising its "almost daily public threats against Cuba".
"They intend to and announce plans to take over the country, its resources, its properties, and even the very economy they seek to suffocate in order to force us to surrender," he wrote on social media, shortly after power returned nationwide.
with reuters
