Thank you for your response, but it is too generalized to answer the question.
Lets dig a little deeper, what electronic components will fail first and why?
Are there any components inside the PSU with some kind of insulation, so that external cooling will not help?
Are there any components with electron diffusion and/or rapid material aging, which will finally lead to failure?
Are the some side effects regarding the software or control units?
Are there any other harmful side effects i do not know yet?
Given your response, I guess you don't know an awful lot about electronics or power supply design.
I've been designing off-line switching power supplies for around 30 years.
You're making the assumptions that the original designers have allowed an overhead in their design of more than 30%, in general this could not be further from the truth. Most of the time designs are made to a price. So components tend to be heaviliy optimised for a particular operating condition, exceeding this will result in failures and these failures are not all down to operating temperature.
It is beyond the scope of a reply to teach you how switching power supplies work and what the weak points are in them. However a simplified list would be
A basic PSU design can be broken down into 4 sections
1) Primary rectification : Consisting of diodes or full FET (transistor, somtimes called an ideal diode) bridge, both approaches will be designed for a particular maximum operating current. Exceeding the specifications of the parts used will result in failure for diode and FET rectification they tend to fail short resulting in the primary fuse going open circuit (assuming the design has one), however in failing they often damage PCB and surrounding components.
2) Power factor correction: Following the primary rectification given the operating power, there will be some form of power factor correction circuit, this will have one or more switching elements consisting of FET's and rectification diodes or other rectification FET, the FET's will again have both voltage and current limits which when exceeded will cause permanent damage to them.
3) Depending on the swiching supply topology and for the kind of power required it is likely a full bridge forward converter or resonant LLC circuit, both of which are heavily complex designs having multiple FET switching elements, snubber circuits and output conditioning and smoothing all designed to meet a particular current and power requirement, you exceed the power design and permenent damage will be done, again not necesarily because of heat, but because you have exceeded the power delivery capablilities of the components in the design.
4) Control loop elements, operational amplifiers, opto-couplers, fixed and variable voltage references, protection and monitoring devices and the switching controller. These elements are less likely to fail but may fail as a result of parts in the power path failing short and delivering high voltages where they do not belong.
Hopefully if the design has been done properly there will be over current and over voltage detection at each stage of the power supply in order to prevent you from destroying the supply by overload, short circuit or by overvoltage.
Damage to components does not come purely from generated heat, although it is a significant factor in the failure of parts due to thermal run-away. Thermal run-away occurs where a part is driven beyond its operating limits and it starts to fail in such a way that it becomes resistive or its leakage current exeeds the devices capability, at which point they let out the magic smoke.
So all in all I reitterate what I said.
Overloading a high capacity power supply is
A REALLY BAD IDEA!
