That PSU doesn't seem to have a control input, so you'll need to do it just be switching the mains input. So either use a relay or an SSR to switch the mains live going to the main PSU.
If using a bare relay you need one with a 5V coil, and you'll need to put a protection diode across the coil. Alternatively, use a 5V relay module or SSR that says it works with arduino.
Note that most of those relay modules don't comply with standards about isolating the mains voltage from the low voltage parts on the PCB, so the result probably won't meet your local electrical safety laws.
If using an SSR bear in mind that all the SSRs on ebay are fakes that don't get close to their stated rating. Buy your SSR from somewhere reputable, and even doing that use one rated two-to-four times your nominal requirement (the SSR rating is for an ideal resistive load with plenty of heatsinking on the SSR). You want a 'zero crossing' or 'zero switching' SSR.
