BTW, old PC PSUs are 'useful' 12V (or 5V or ...) power supplies - they can run garden lights (take sensible weather/water/safety precautions!), and act as a useful power source for small 12V appliances, chargers, electronic circuit experiments, etc. You can even use them as 'car battery charger supplies' - you can tweak the output voltage slightly, and then feed the power thru a 'charger controller circuit' - you can get 10 - 20 amps at 12 V out of some PSUs!

Some sort of load on the lower voltage buses may usually be needed, depending on the actual (switching power supply circuit) design (a high wattage resistor, or even a lamp! - power on indicator???!!!), and a 'power on' momentary switch as in "use a bit of wire to emulate the on switch***"... actually there are a lot of articles around in Electronic/PC_modders magazines, and on the net about this sort of 'conversion'... some guys even use them to run Xmas decorations, (motor power supplies for animated Santas, etc)

Surprised that no 5V output is on that PSU - the 'drive power plugs' have both 12V & 5V circuit.

*** for AT supplies - old XT PSUs were slightly different...