Use Kapton (Polyimide) high-temperature tape to re-close the PSU case. Depending on the tape, you might have to use your fingernail or a spudger to press on the tape so the adhesive makes good contact with the plastic case.

As an extra safety measure, you can add a loop of Kapton tape over one (or both) of the insulated wires. Make the loops very loose, else you will not be able to twist the plug back into the case.