5V DC to 12V DC Is this posable ?

You can find DC-to-DC converters that can do the job. But first you have to find out whether the USB connector can provide enough power. IIRC, the typical spec is around 50 mA at 5 volts, although with a wall-wart-powered USB bus, I think you can get up to 200 mA. You don't say what power or current the fans require.

I suspect it will be cheaper and simpler if you just go buy a 12 volt wall wart to power your fans. I usually go to the local thrift stores, as they often have boxes of wall warts for 50 cents or a dollar apiece.

 

What is the current rating on the fans? USB power is rated 500 mA MAX at 5 volts. This gives (amps * volts = watts, 0.5 A * 5 V =) 2.5 watts. If your fans are rated above 200 mA current draw, you're going to need an external power supply. If you want to build one yourself, you're looking at a transformer and rectifier, minimum. You might look around for an extra 12v DC wall wart with an amperage rating that can handle both fans (and then some).

Edit: Whoops. Guess daddles got to you before I did.

 

Or simply just use the 12V fans directly at 5V (most will start & run) for a gentle quiet breeze. It doesn't take much of a flow to cool equipment appreciably.

 

I've pulled 12V DC fans out of Dell computers that pull over 1500 mA... Best to check the ratings on that fan if you're going to straight-up plug it into USB...

 

First of all, live and neutral denotes mains AC current, like you would typically find in a wall outlet. Please don't plug one of these fans straight into the wall.

You would be wiring the +5V and 0V (i.e., ground) of the USB connector to your fan. You could try touching the leads to a 9V battery (just for a short amount of time) to help you figure out which lead is which.

Yes, as long as the voltage rating of the fan is +5VDC, and the current rating is under 500 mA, you should be fine. Keep in mind, your current limit might be lower if those USB ports are connected to anything else that needs that power.