When you say computer grade supply, you don't mean one from a PC do you?
If it is a power supply from an old Mini (mine is from a Wang system) you may find there is an adjustment pot. Have a look at the regulator board.
The one I have allows adjustment from 11 to nearly 16 volts @ around 40 amps.
If you starve an amp for voltage (what happens when it can't get the current it will need, voltage drops), the quality of the audio suffers.
Does the PS deliver 12V or closer to 14V?
12V is on the low side, most like about 14V, what a car typically gives.
I'll have to get a volt meter to check the output but i was told 12 volts.
those computer power supply wattage/amperage ratings are for the combined 12v 3.3v and 5.5 volt lines , the actual 12 volt amperage may be 1/2 of what the combined spec may be , or less .