miniITX power supply for ATX motherboard?
I am in research of powering my future carPC. Have decided a motherboard to be ATX or at least miniATX. Need a power supply. Inverter is not an option, as it uses up to 25% of delivered energy just to power itself. Best DC-DC power supplies are for miniITX systems. And I want to use miniITX power supply for an ATX motherboard.
So I see that ITX and ATX power plug specifications differ in wires count and also 3V (mITX) or 3.3V(ATX) wires. ITX connector has 2 rows of 10 wires and ATX has 2 rows of 12 wires. So ATX has 4 wires more: +12V, +3.3V, +5V, COM. And ITX doesn't use one wire , where ATX has -12V (strange voltage, if you should ask me).
And my questions are:
1. Can I take +12V from another +12V wire, or they are separately regulated in ATX and would make system unstable or even burn down some part?
2. Does it matter so much if there is +3.3V and I can take +3V instead? Integrated circuits should be same type on both ITX and ATX motherboards, right? So it is maybe just written in specification +3V, but is really meant +3.3V.
3. What is that -12V on an ATX for a wire and can something be done about it?