x2 Bean420. Some amps are legit down to 9v!!! like sound digital.
It is Power regulated power supply VS non regulated ones. With regulated amps they will comphensate for the voltage drop and still put out rated. The other type will allow you to get more power or less varying on voltage. Competition amps for SPL comp will usually be in un-regulated, but can be either way. With music it is nice to be regulated. If you drop in voltage i believe your amp draws more current.
IMO screw 14 and above volts unless you are money bags.