The 7500 has a different arrangement of signals in the power connector.
The 7500 uses a different power connector -- actually two power connectors, where the ATX in the Beige uses one.
The power connectors have different numbers of pins.
The Beige G3 runs it's power-hungry circuitry on 3.3V where the 7500 uses 5V for those components. Therefore the 7500 has inadequate 3.3V supply for the Beige G3.
In order to turn the power supply 'On' in the 7500 the logic board ties the "Power On" pin to the 5VSB pin. In order to turn the power 'On' in a Beige, the logic board ties the "Power On" pin to Ground.
You may not find a power supply that is the exact shape, but small powerful ATX supplies abound which can be fit into the Beige G3 case. For example this might be close, although the power available is a little low: http://cgi.ebay.com/Gateway-E4000-Small-Form-Factor-P4-Power-Supply-6500696_W0QQitemZ400085097058QQcategoryZ3670QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D20%26pmod%3D400102982379%26ps%3D63%26clkid%3D6127263069489856293
And a little shopping on Newegg or at Frys will turn up all kinds of others.
The 7500 uses a different power connector -- actually two power connectors, where the ATX in the Beige uses one.
The power connectors have different numbers of pins.
The Beige G3 runs it's power-hungry circuitry on 3.3V where the 7500 uses 5V for those components. Therefore the 7500 has inadequate 3.3V supply for the Beige G3.
In order to turn the power supply 'On' in the 7500 the logic board ties the "Power On" pin to the 5VSB pin. In order to turn the power 'On' in a Beige, the logic board ties the "Power On" pin to Ground.
You may not find a power supply that is the exact shape, but small powerful ATX supplies abound which can be fit into the Beige G3 case. For example this might be close, although the power available is a little low: http://cgi.ebay.com/Gateway-E4000-Small-Form-Factor-P4-Power-Supply-6500696_W0QQitemZ400085097058QQcategoryZ3670QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D20%26pmod%3D400102982379%26ps%3D63%26clkid%3D6127263069489856293
And a little shopping on Newegg or at Frys will turn up all kinds of others.