BillWD
The XPS 8300 requires a power supply with four SATA power connectors, the 650 Watt ZUMAX ATX 12V 2.0 Power Supply specifications, say it only has two:
1 x power 24 pin ATX with detachable 4 pin section ¦ 2 x 15 pin Serial ATA power¦ 1 x power 8 pin EPS12V with detachable 4 pin ATX12V section ¦
4 x 4 pin internal power (fan only) ¦ 6 x 4 pin internal power ¦ 2 x 4 pin mini-power connector ¦ 2 x 6 pin PCI Express power.
4 x 4 pin internal power (fan only) ¦ 6 x 4 pin internal power ¦ 2 x 4 pin mini-power connector ¦ 2 x 6 pin PCI Express power.
To use this PSU in the XPS 8300, you would need to buy 2 x 4-pin Molex to SATA power adaptors.
Regards to using the Radeon HD 7750 video card, there should be no need to upgrade the default 460w unit, I am using the same Radeon HD 7750 video card in an Inspiron 530 MT with the default 300w PSU without any issues.
Bev.