That sounded strange to me, since Brazil imports power from Uruguay and Argentina through somewhat small DC links, and if only them failing is enough to cause a blackout in Brazil, something was probably not configured correctly. So I went looking, and according to https://g1.globo.com/mundo/noticia/2019/06/16/apagao-deixa-m... "deixou sem energia toda a Argentina, Uruguai, Paraguai e sul do Brasil", so Paraguay was also affected. Paraguay shares the huge Itaipu dam with Brazil, and a large amount of power in Brazil comes from the Itaipu dam, so if Paraguay was affected, Brazil (mostly the south and southwest) will probably also be affected.
edit: the realtime graphs at http://www.ons.org.br/pt/paginas/energia-agora/carga-e-gerac... show a loss of around 1.3 GW of hydroelectric generation in the south region starting around 7:00 and ending around 10:00, matching the timing of the blackout.
According to Paraguayan news [1] (Spanish), the failure was on the Argentina side of the Yacyretá hydroelectric (which is shared by Argentina and Paraguay), not at the plant itself. Only a few Paraguayan towns close to the hydroelectric itself were affected, while Argentina and countries it resells electricity to were out of power.
That sounded strange to me, since Brazil imports power from Uruguay and Argentina through somewhat small DC links, and if only them failing is enough to cause a blackout in Brazil, something was probably not configured correctly. So I went looking, and according to https://g1.globo.com/mundo/noticia/2019/06/16/apagao-deixa-m... "deixou sem energia toda a Argentina, Uruguai, Paraguai e sul do Brasil", so Paraguay was also affected. Paraguay shares the huge Itaipu dam with Brazil, and a large amount of power in Brazil comes from the Itaipu dam, so if Paraguay was affected, Brazil (mostly the south and southwest) will probably also be affected.
edit: the realtime graphs at http://www.ons.org.br/pt/paginas/energia-agora/carga-e-gerac... show a loss of around 1.3 GW of hydroelectric generation in the south region starting around 7:00 and ending around 10:00, matching the timing of the blackout.