Berkshire Hathaway said last month that it would buy Oncor for $9 billion, and last week it stuck to that bid.
Hedge fund Elliott Management, which owns a significant portion of Oncor's debt, opposed Berkshire's takeover bid, saying it wasn't enough.
Elliott spokesman Michael O'Looney said the hedge fund supports Sempra's bid because it will provide more to all of Oncor and Energy Future's creditors.
Previously, in April Texas regulators rejected a proposed $18 billion sale of Oncor to NextEra Energy Inc. That price tag included debt.
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