My Electronics is pretty buggy at the moment. But I will tell you what I know. Its ok to run your Amp from a PC PSU (SPMS) - but you need to kind the right kind of Amp and SMPS. Your Amp should not use dual power supply (+12V, 0V, -12V).. because as you pointed out -12V in PC SMPS is not having enough Ampheres to power your Amplifier. The -12 V in SMPS is used for serial communication in PC's as far as I know. So if you use -12V, expect the SMPS to catch fire.. But if your Amplifier uses only +12V and GND (ground), you might be in luck.. Most SMPS available today could have enogh juice to power your Amplifier.. You should know that this is an option if you have a spare PC SMPS.. If you are buying a new SMPS, you could buy a SMPS specialized for your Amplifier...