timkolson:
I am driving a single 16ft led rgb strip using IRLB8721 N channel mosfet's, with a 12v 5a power supply connected to the barrel jack on the uno. The VIN is connected to the +12v lead on the rgb strip.
Not ok.
There is a reverse protection diode between the DC socket and V-in with a max rating of 1Amp.
Drawing more than 1Amp through the Arduino board will eventually fry that diode.
That diode also has a volt drop of ~1volt@1Amp, that will make your strip less bright.
Power the strip (12volt and GND/mosfet) directly from the supply, and the Arduino through the DC socket.
Leo..