The last two years have been hard on Argentina and Brazil. A sweeping corruption investigation and the impeachment of President Dilma Rousseff have sent Brazil's currency tumbling. The country's economy contracted by 3.8 percent in 2015 and by another 3.6 percent the next year. The Argentine peso, meanwhile, fell 40 percent against the U.S. dollar after the government lifted currency controls in late 2015. But for foreign investors, the two South American nations' economic hardship presents an opportunity. The depreciated currencies in both countries, combined with their governments' need for investment, has enabled Chinese companies to buy up cheap assets and launch major infrastructure projects in Argentina and Brazil alike. The electricity sector in particular has been a focus of their activities....