Is it the power supply

[Kevin_332]

Hey I did house audio setup using a 5000w monoblock it is connected to a dc regulated power supply 12v at 10 Amp stable but the power fluctuates on the amp so it dips with a capacitor work

 

[americanaudiophile]

A cap would stabilize the voltage if the power supply is sagging (which it is) but maybe not enough to make that much difference.
12 volts at 10amps is 120 watts. With a 100% efficient amp (which doesn't exist) you would need about 417 amps at 12v to produce 5000 watts.
The good news is the power rating on your amp may be pretty much a pie in the sky number so you probably don't need that much. If the amp has an inline fuse to the 12 volt input that would be the max amperage the amplifier can take. Use that as the amperage the 12v supply needs to deliver to get max power out of the amp.