Social media posts suggested equipment from Poland was appearing on Ukrainian online marketplaces.
However, officials say the generators pictured have different power specifications from those sent as aid.
"We can control how they are being used," Tomasz Kułakowski from Poland's Interior Ministry told the Polish News Agency (PAP).
He said each generator has documentation including serial numbers, warranty cards and product specifications.
The Stand with Ukraine foundation, which organised the "Warmth from Poland for Kyiv" fundraiser collecting nearly PLN 9 million (EUR 2.1 million), has sent 230 generators to Kyiv, with more ordered.
Foundation president Natalia Panchenko said none of the equipment shown in the online posts matched their donations, noting the 600kW generators they sent were not visible in the images.
Poland's government separately sent 379 generators and 18 heaters to the Kyiv region on 23 January, following Russian attacks on Ukraine's energy infrastructure during a cold snap.
The generators have a maximum capacity of 115kW.
Producer Tomasz Błaszak, whose company FOGO supplied 108 units to the foundation, said the equipment model had never been offered for sale in Ukraine before and would be easily recognisable.
Both the foundation and the interior ministry said contracts prevent donated equipment from being resold and allow for inspections at any time.
Kułakowski described the social media posts as "typical disinformation targeting Polish solidarity with Ukraine".
Similar false claims about misused humanitarian aid have circulated previously, including allegations in 2023 about donated ambulances.
(ał)
Source: PAP