The original HP dc7100 CMT convertible Tower model comes with a 340watt active PFC power supply unit. I realise the position of the 4 screws securing the HP original PSU is different from any of those ATX form factor Power Supply Unit. A standard ATX PSU with the fan at the back (right sided) will have the fan partially blocked by the chasis at the right side. That is why the HP original PSU has the fan almost in the center looking from behind. To address the fan issue, I may have to buy a PSU with those big 120mm fan facing downward instead of facing behind, but the screw holes are still quite diffrent. Could anyone advise if such standard ATX psu could be used in a HP dc7100 tower model? Apart from the physical positioning of the screws and fans behind, is there any other specifications ie. Active PFC type versus no PFC in a std ATX psu. I really appreciate if those who have used std ATX power supply for HP dc7100 Tower model as replacement or upgrading to higher power, pls share and advise. Thks