Ray Jennings, a former South Africa international wicketkeeper, only saw his son had made a ton against India when his power returned an hour later.
"When he reached 96 the electricity went off, so I missed his hundred," he told BBC Radio Newcastle.
"When it went back on an hour later, I watched one ball and then he got out."
Durham left-hander Keaton, whose mother was born in Sunderland, became eligible to play for England in 2016 after serving a four-year qualification period.
The 24-year-old opener top-scored with 112 as England ended day one on 288-5 in the fourth Test against India.
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Asked what he said when the power went off, Jennings Snr said: "I'm sure a lot of your listeners would know it wouldn't have been a long sentence - it would've been short and abrupt, but I wouldn't be able to repeat it on air.
"It was a little bit of a bitter ending, but I'm very happy to know he actually ended up getting a hundred.
"Keaton keeps on telling me that one of the things I've done well is marry a British lady, so she's [his mum] over the moon and Keaton's over the moon.
"I've suddenly moved away from supporting a South African side to supporting an English side, and I'm very proud to actually say that.
"It's probably the most enjoyable sporting day I've ever had - for someone in your own family to achieve something like that has really been a blessing for me."
Keaton Jennings' dad Ray says he missed his son's England debut century because of a power cut while he was watching the Test on television in Mauritius.