The Zumax ZU400W model of the X1 series, is just a regular Switched-Mode Power Supply.
Budget unit with low quality hardware components inside,http://www.zumaxpower.com/products/zu400w.htmhttp://www.directron.com/zu400w.html
1) Low quality Electrolytic Capacitors
2) Low quality MOSFET's.
3) Low quality Rectifier Bridge
4) Wiring is small gauge.http://en.wikipedia.org/wiki/Switched-mode_power_supplyhttp://en.wikipedia.org/wiki/File:ATX_power_supply_interior-1000px_transparent.png
Weakest link are the Electrolytic Capacitors.
It is because of the Electrolytic Capacitors, that there is a electrical hazard warning on the case.
An Electrolytic Capacitor can hold a charge for weeks, months, sometimes over a year, when removed from power.
If the 'tech' comes in contact with the terminals (Leads) of a capacitor, and it is charged, the charge can be released to the 'tech'.
If the 'tech' completes a circuit with their fingers, that one or more capacitors are in, the charge can be released to the 'tech'.
Shock can be bad to fatal.
Capacitors are Properly discharged before working on the unit.
In the Power Supply cutout look at the letter B.
This is a top view of two large Electrolytic Capacitors. These two are used in the Input Stage.
Incoming AC electricity is filtered by these two 'Caps'.
They are probably rated at 100 to 160 Volts.
Think what will happen if they are not properly discharged, and your fingers touch their leads. (Or complete a circuit they are in)http://www.smpstech.com/tutorial/t00con.htm
The capacitors used are Radial Aluminum Electrolytic Capacitors.
For additional questions please post in a Comment.