Aero Specialties PS 100 28V Aircraft Power Supply. Low use and In excellent condition. Price is $1875.00 + Shipping.

Here is a link on Aircraft Spruce with a detailed description. https://www.aircraftspruce.com/catalog/elpages/powervampps100_11-20079.php?clickkey=11165278

Is voltage adjustable at all?

I don't believe so, but here are the specs...
Output current: 100A
Output voltage: 28VDC
Output ripple: ˂150mV p-p
Input voltage: 90-264V AC/47-63Hz
Input current: 16A @ 230V AC, 32A @ 115V AC/single phase (typical)
Operating temp.: -20°C to +50°C (-2°F to +122°F)
Case: Aluminum with shock-absorbing feet
Voltmeter/Ammeter: Solid state LED, IP65
Aircraft cable: 2m (6ft) with heavy-duty rubber NATO connector
Input cable: 1m (3ft) with 16A 3-pin 6h blue plug
Cooling: Forced ventilation
Protections: Thermal, current overload, short circuit, over voltage
NCAGE: KD628

Even without seeing the insides I can pretty much guarantee that the output voltage is adjustable but probably only over a small range like +/- 10 or 15%. It just wouldn't make sense to design something like this without a way to tweak the output. It's probably just as likely that it's not possible to convert it to 14v unless it was specifically designed for that capability, which I doubt.