How to use a standard 24-pin or 20-pin ATX power supply for a 22 pin power supply (e.g. Mac G4 Gigabit Ethernet)
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24-pin ATX power supply connector
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22-pin ATX power supply connector 
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Finding a 22 pin power supply was hard for me; so, I just re-used a power source from an old Windows machine (a 20 pin, but you could easily use a 24 pin as well); AND, note that the standby pin #22 states 28 Volts but I got mine to work with the standard 5V (i.e. no need to jump voltage from 5V to 14V or even 28V). Also note, make sure the power source fits (i.e. the power plug lined up with the back of the G4 opening for the power plug). I also found the above table and image online; please reference just in case your colors don't match (as wire color means nothing, just helpful).
Clip off the 22 pin connector (you know, give yourself a couple inches to work with) from your dead power supply and clip off the 20 pin connector from the good power supply and unsheathe a centimeter from all the ends of the wires (using a wire stripper tool). Then attach the various wires by twisting them together and then tapping them up with some electrical tape.
- connect the power source orange and small gauge brown (+3.3V and smaller gauge 3.3V sense on pin #13) to the orange and brown (pin #1) on the harness connector
- tape off the power source grey (would-be power good on pin #8); i.e. won't be using this power supply wire
- connect the 2 power source orange wires (+3.3V pin #1 and #2) to the 3 orange wires (pin #1, #2, and #8) on the harness connector (and if using a 24-pin power supply, i.e. will have an extra orange wire, just have three pairs of orange wires)
- connect the power source green wire (power on pin #16) to the harness connector green (power on pin #15)
- connect the power source yellow wire (+12V on pin #10) to the harness connector yellow (+12V on pin #10) wire
- connect the power source blue (-12V on pin #14) wire to the harness connector blue wire (-12V on pin #13)
- tape off the power supply blue wire (would-be optional -5V on pin #20); i.e. don't need a -5V from the power source
- connect the remaining 7 black power supply wires (ground on pin #3, #5, #7, #15, #17, #18, and #19) to the remaining 8 black wires (ground on pin #3, #5, #7, #11, #14, #16, #17, #18, and #19) on the harness connector (and if using a 24-pin power supply, i.e. will have an extra black wire, just have eight pairs of black wires)
- also, I sacrificed the floppy drive power connector (smaller white plastic connector with the same four wires as the other standard molex connectors that you power up your hard drives or optical drives with) to hook up the fan connector: tape off the extra black wire and red wire and connect one of the black wires to the black wire of the fan connector and the yellow wire to the yellow wire of the fan connector.
- finally, we need 28V of standby power (or power that trickles out of the power source when it's off; so, no bright ideas of just using a 12V yellow connector which is only juiced up when the power source is on, not just plugged in); so, we connect the power source purple wire (+5V standby on pin #9) and connect it to the white wire (+28V on pin #22) on the harness connector and hope it's enough!
If not enough, you need something to jump or multiply the voltage: try the power button green board from the old Blue and White (a.k.a green) G3 Macs, which had said functionality (i.e. will jump 5V to 14V, which will definitely be enough; i.e. no need to jump to 28V). Find one and note the smaller gauge three wire (red, black, white), and all wrapped in a grey sheathe. You will also have to use a couple spare blacks and red wires (in addition to the purple wire) from the power source (sacrifice a molex connector like the fan connector hookup in the previous step). Connect the two spare black power source wires to the black wire from the old G3 power button board. Connect the purple power source wire to the red and white wires from the old G3 power button board and to the white wire (pin #22) on the harness connector.