Legal Question in Technology Law in California

Re: U.S. Mail Laws and Regulations

The second computer is not a gift and it isn't yours. You must return it, at the sellers request and expense.

You may be confusing your situation (too much merchandise shipped by mistake) with the rule that lets the recipient keep unsolicited merchandise mailed to them in the hope of making a sale or encouraging a donation.

The difference is that the shipping of the unsolicited merchandise was no mistake, it was intentional. Items shipped by mistake must be returned upon request and at the sender's cost unless two things are true: (1) you did not know of the mistake, e.g. you bought 2 pounds of goldfish food and they shipped you a kilogram (2.2 pounds)instead and you didn't notice the extra weight, and (2) you have "materially altered" your position in reliance on your good faith and reasonable reliance upon the correctness of the shipment, e.g., you already fed 1/2 of it to the fish so it cannot be weighed any more to verify the quantity.

(Not a perfect analogy, but it's good enough to illustrate the concept).