The extra connector is simply additional 5 and 12 volt power supply lines.
These allow for the additional current requirements of newer CPUs.
I would be more concerned about the high wattage rating of the supply.
Unless you have a number of drives installed, a 400 watt supply has nearly twice the power capacity a supper socket 7 system needs.
Theoretically, all this means is that the power supply will not be working very hard, and will run much cooler than a 250 watt supply.
In practice, if the supply is poorly (cheaply) designed, it may have voltage spikes on the output lines when it starts up.
If there are spikes on the supply lines, it will be more of an issue for your drives than the motherboard.
Bottom line, if it is a name brand supply you should be fine.
If it is a no name supply and is noticeably lighter than other 400 watt power supplies, there "may" be some slight risk.
Chas