MoreDell logos are seen at its headquarters in Cyberjaya, outside Kuala Lumpur in this September 4, 2013 file photo.
The ruling, which applies to about 5.5 million Dell shares, is a victory for the specialized hedge funds that have increasingly tried to squeeze more money from mergers using a type of lawsuit known as appraisal.
The judge dedicated much of the opinion to explaining why deal price was not a fair value indicator, particularly in a management-led buyout.
About 3.9 million appraised shares were held by affiliates of Magnetar Capital.
A small number of hedge funds have built a strategy of swooping in just before a deal closes, when there is less risk a deal would collapse, and buying stock for the sole purpose of seeking appraisal.
Dell was able to knock out T Rowe Price's stock, which comprised the bulk of the shares in the case, because the fund manager mistakenly voted in favor of the buyout.