Power supply damages motherboard when a computer assembler
purchases power supplies without consulting specifications.
Intel specs for ATX power supplies demand that PSU not damage
motherboard and other components:
Section 3.5.1 Overvoltage Protection
The overvoltage sense circuitry and reference shall reside
in packages that are separate and distinct from the
regulator control circuitry and reference. No single
point fault shall be able to cause a sustained overvoltage
condition on any or all outputs. The supply shall provide
latch-mode overvoltage protection as defined below.
Table 11: Overvoltage Protection
Output
+12 VDC Max is 15.6 volts
+5 VDC Nominal is 6.3 volts
+3.3 VDC Nominal is 4.2 volts

Too many computer assemblers don't have necessary technical
knowledge and therefore don't even know that overvoltage
protection (OVP) has been a defacto standard for 30+ years.
That motherboard damage probably may be traceable to the
ill-informed computer assembler (who does not demand specs) or
a power supply manufacturer who outrightly lies on his
specifications.

There is nothing in a UPS that will accomplish the necessary
OVP.

Other essential functions that should be found in the power
supply specification, but that many 'bean-counter' selected
supplies may be missing:
Specification compliance: ATX 2.03 & ATX12V v1.1
Short circuit protection on all outputs
Over voltage protection
Over power protection
EMI/RFI compliance: CE, CISPR22 & FCC part 15 class B
Safety compliance: VDE, TUV, D, N, S, Fi, UL, C-UL & CB
Hold up time, full load: 16ms. typical
Efficiency; 100-120VAC and full range: 65%
Dielectric withstand, input to frame/ground: 1800VAC, 1sec.
Dielectric withstand, input to output: 1800VAC, 1sec.
Ripple/noise: 1%
MTBF, full load @ 25°C amb.: 100k hrs

Power supplies missing these and other functions are sold at
good profit in the North American computer clone market. OVP
must be in all computer supplies but is often missing in clone
computers.


"J.J." wrote:
If a computer PSU fails then I have heard that it may (or may
not) blow the mainboard and perhaps various other components
with a power surge or soemthing like that.

It seems that better PSUs are designed so that when they fail
they have some circuitry which protects the other components
in the PC.

Is this failsafe feature of the PSU I am referring to pretty
much the same feature you are referring to? Or are they
separate features?

Does anyone know how common it is to get this failsafe
feature in a PSU?