Is this UPS Socket Defective?
That is a valid type of socket. See the APC manual for the BX-1400 MS.
However, I would be extremely careful plugging any US type B plugs into this UPS. As far as I can tell, this is a 230V UPS. The US type B (aka NEMA 5-15) is normally used for 120V devices. If your device comes with a type B plug and, like most but not all computers, monitors and laptop power bricks made in the past several years is rated for 100V - 240V (or similar) then this will work fine. However, if you have a device that requires 120V (or 100V - 125V) power, using it with this UPS is a very bad idea.
All that being said, if the socket on one UPS works correctly and on another it does not, take it back to the store.