Electronics, especally PSUs, can emit a number of different smells.
When they wave solder a PSU, there is flux used to help remove and prevent oxidation and improves the viscosity of the solder. This flux leaves a residue on the PCB that can be cleaned off, but it's almost impossible to clean it all off without damaging some SMT. When the PSU is run, and it gets hot, this flux heats up and emits a smell (smells like burnt plastic). Eventually, all of the flux is burned off and the smell goes away. But it takes time.
On that same subject....
There is "no-clean flux" out there, but it's not commonly used because it costs twice as much. FYI: If you've had electronics that smell "fruity", that's because they use no-clean flux.
And FYI: If you have electronics that smell like isopropyl alcohol, that's because they used the alcohol to clean the flux.