OK, forgive my ignorance but:

A big capacitor would possibly help, but it got to big enough to supply those few amps long enough for the motor to start spinning up.

That it is not really able to deliver 12 volts at a full 7amps. In that case a capacitor of adequate size across the supply will be one way to make it start.

A large capacitor MAY be of assistance

Wouldn't a cap (I'm envisioning across the + & - of the supply) act like a dead short at the moment power is applied? Wouldn't that demand infinite current (theoretically)? A cap in parallel to the load will still act like a dead short. If applied in series on a DC supply, the cap will run the motor until charged then stop all current from passing. Am I wrong? I'm wondering in what configuration a cap would be of use. Even if the switch controlling the motor is after the cap - still, when the PS is turned on wouldn't the cap, which should be fully discharged by now act like the same, afore mentioned, short?

 

A model of a large capacitor may draw an infinite current when first connected to a power source with zero internal resistance. In the real world all capacitors have some ESR, (equivalent series resistance, and all power sources have internal resistance. And most power supplies have some current limiting internally, and certainly the one that the TS was using dropped the voltage when the load was more than it could handle. The challenge with using a large capacitor to supply starting current is that motor starts take a lot more than an instant. So the capacitor gets large, both in size and in cost.

 

A model of a large capacitor may draw an infinite current when first connected to a power source with zero internal resistance. In the real world all capacitors have some ESR, (equivalent series resistance, and all power sources have internal resistance. And most power supplies have some current limiting internally, and certainly the one that the TS was using dropped the voltage when the load was more than it could handle. The challenge with using a large capacitor to supply starting current is that motor starts take a lot more than an instant. So the capacitor gets large, both in size and in cost.

I found out that in order for the DC motor to start it requires a surge of 5 Amp of current or probably a little bit more and when it runs only around 1.5 amp is needed. So i guess the SMPS power supply that i use was not capable to accommodate that surge current need to spin the DC motor at the initial start

 

The correct way to measure the armature current at start up, is to use a LV known DC value supply to the motor and measure the current with the rotor locked,
Take a few readings at different positions and take the highest amperage reading to calculate the armature resistance.
Max.

 

The correct way to measure the armature current at start up, is to use a LV known DC value supply to the motor and measure the current with the rotor locked,
Take a few readings at different positions and take the highest amperage reading to calculate the armature resistance.
Max.

The end solution to this actually is to remove the over current / over voltage circuit protection of the ATX power supply now it works 100% perfected without fail