I am sure it is a faulty charger. I had the exact same issue TWICE! Worked fine and then it would do as you describe (blinking when phone plugged in). Lucky for me I had Microsoft complete. Called them and had a new charger in two days with NO QUESTIONS asked! Plugged it in and viola all worked fine. Still on my third, with no issues so far.
Did you by any chance changed the USB cable used for charging, or your actual smartphone, between your first two chargers and the newest one ? I am pretty sure that it works with a standard USB cable (not designed for charging but will still charge at 5W - 5V and 1 Amp) but it doesn't work with 10W (5V-2Amp) cables.