Can I use a USB connector/plug for RGB Led Strip
No

USB is specified with a maximum of 2.5W (500mA @ 5V) and this is only after the devices exchanged this information and the software allows it.

If you're talking about the plug itself: It can probably handle the current but one day you'll plug it into your PC because you forget about that .. special .. USB plug and it might fry your internals. Do not use plugs for purposes other than they are intended for.

Go get some standard Molex connector which doesn't have a special "function". How do you plan to switch your LEDs on and off anyway?