Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

Portugal is supplying electricity to clients from its own sources as power exchanges with Spain remain suspended amid an inquiry into the causes of a blackout earlier this week, the energy minister said on Friday.

One of Europe's most severe blackouts grounded flights, paralyzed metro systems, disrupted mobile communications and shut down ATMs across the Iberian Peninsula.