Partition problem with distinct integers
Here is an outline of a reduction from PARTITION to UNIQUE PARTITION. Suppose the original numbers are $x_1,\ldots,x_n$ and the target is $T$. I assume that all $x_i$ are positive integers. The new numbers are going to be $2^n x_i + i$, as well as $1,2,4,\ldots,2^{n/2}$, and the new target is $2^n T + 2^{n/2}$. (The numbers $2^n,2^{n/2}$ are quite arbitrary and could be made much smaller.)