Without a 3.5 digit multimeter, then you don't know if voltages are
OK. Important are voltages on any one of each purple, red, orange, and
yellow wires that should exceed 3.23, 4.87, and 11.7 volts. What are
(and post) your voltages?

Handshaking involves green and gray wires. Voltage on green wire
should exceed 2.0 volts before switch is pressed and drop to less than
0.8 when switch is pressed. Gray (power good) should exceed 2.4 volts
within seconds after a switch press.

If Power Good does not remain stable, then meter should identify
which red, orange, or yellow wire voltage is going defective first.

None of the above voltages can be confirmed without being loaded by
the computer and without a digital meter or something equivalent (and
more expensive). These tests are best performed when computer is
accessing all peripherals (multitasking).

wrote:
...
My PC went dead (no display, but the CPU fan spins). Looking at this, I
naturally suspected the motherboard, but then I found the system works
fine with another poer supply.

Funny thing is, the defective(?) power supply seems to give all the
voltages all right, but just doesnt start up the system.

Could this be a 'power good' signal issue? If it is can it be tested?

Another pointer: earlier, the CPU fan would initialise only after
pressing the soft-on power supply switch on the mobo. Now, it starts
the moment the system is powered up. On the other hand, if no load is
connected to the PS, it seemingly behaves exactly as it should; off
till soft switch pressed (green wire connected to ground).

Before buying another supply, I'm wondering if there is anybody has
seen this specific problem, and managed to fix it?