Here's a way to remember voltages from AT / ATX power supply units.
Remember the word BOWRBY (bow-re-bii), its an acronym for the coloured wires coming from the PSU.
Black _ 0v
Orange _ +3.3v
White _ -5v
Red _ +5v
Blue _ -12v
Yellow _ +12v
and just the few odd ones,
Grey _ Power_good (+5v)
Purple _ +5v Standby
Green _ PS_On (Power Supply on signal)
AT form factor uses two 6-pin connectors typically identified as P8 and P9, but may be identified as P1 and P2.
ATX uses one 20-pin connector.