AES is discussing the sale with Sev.en Global Investments, the financial vehicle for foreign acquisitions of Czech energy firm Sev.en Group, ultimately owned by billionaire Pavel Tykac, the two people told Reuters, declining to be named because no deal had been finalised yet.
It was not clear if AES was in talks with other potential buyers.
The plant's second-largest shareholder, South Korea's energy firm Posco International (047050.KS), told Reuters it was also considering selling its 30% stake, but did not elaborate further.
AES had no immediate comment. Sev.en declined to comment.
AES is one of the U.S. largest investors in Vietnam, mostly involved in the coal power business there. Its divestment would come as chipmaker Intel (INTC.O), which also runs a major operation in the Southeast Asian nation, shelved a planned expansion there.
U.S. President Joe Biden visited Vietnam in September and signed deals to boost investments in the country. AES wants to build a liquefied natural gas (LNG) terminal and gas-fired power plant in Vietnam.
AES had tried to sell its 51% stake in the 1.2 gigawatt Mong Duong 2 coal-fired power plant in 2021 but the deal fell through after the company said it signed a sale agreement with a consortium led by an undisclosed "U.S.-based investor".
The sources did not say how much AES's stake could be valued at under the current deal being considered.
Posco's 30% stake was valued at $185 million when it had tried to sell in 2021, according to a regulatory filing from the company. That deal, which collapsed like the AES one did, would have valued the plant at over $600 million.
Sovereign wealth fund China Investment Corporation (CIC), which owns the remaining 19% stake in the plant, is considering selling under the terms agreed by AES with potential buyers, one of the sources said.
It is unclear whether CIC was also considering a potential sale to a possible buyer of Posco's stake.
CIC did not reply to a request for comment.
The ownership of the Mong Duong 2 plant is scheduled to be transferred to the Vietnamese state by 2040, a quarter of a century after it began operations.
Vietnam wants to end power generation from coal by 2050, under commitments that have attracted funding pledges from Group of Seven (G7) members and are expected to be fine tuned at the UN Climate Change Conference which begins on Nov. 30 in Dubai.
Sev.en is focussed on acquiring coal assets and other fossil industries as their prices drop amid the global trend to phasing them out - a business strategy that environmental activist Greenpeace said made the company a "climate change villain" .
"Without doubt this will end one day, but at the moment there are opportunities in this sector," Tykac, whose net worth Forbes estimates at $8 billion, told Reuters in May.
Reporting by Francesco Guarascio @fraguarascio in Hanoi and Jan Lopatka in Prague; additional reporting by Khanh Vu in Hanoi, Ju-min Park and Joyce Lee in Seoul, Roxanne Liu in Beijing; Editing by Raju Gopalakrishnan