250W RMS Sub / 150W into 4 ohms Amp - Which PSU wattage should I pick?

[n3onis]

I'm going to connect a 250W RMS subwoofer to a 150W into 4 ohms Amplifier. I want to connect the amplifier to a computer, so I will need another power supply to do that.
- Should I look at the wattage of the amp or the subwoofer when buying a PSU?
- Can I connect a let's say 300W PSU to a 150W amp, or do I have to keep it at limit?

 

[n3onis]

I found out that the PSU should have the same or a bit higher wattage than the amplifier, as spikes do happen.
So for a 150W amplifier, I'm gonna get a 250W power supply.

 

[americanaudiophile]

If the sub amp has a AC power cord then you don't need another power supply (it has one built in) to connect it to the PC subwoofer output.
If you mean that you are going to use a car amp to drive the sub and need a power supply for it then I would go to at least 350-500 watts. No amplifier is 100% efficient at converting PS power to audio amplifier power. If the amp is digital then it will be more efficient (maybe 90%) but if it is old school analog then it could be 40-50% efficient.