DIY Cooling RT-AC86U, Is it safe? Increased lifespan?

I just put these two fans on the back of my AC86U router (left). The bigger one is 140mm and the smaller one is 120mm. These were spare fans from my PC laying around so I thought of utilising these in this way. Connecting the fans to USB ports make the fans run very slow so I bought a 12V AC to DC adapter from the market and connected the wires of both fans to that adapter.
The router isn't even getting warm on touch when these are powered on. I...

DIY Cooling RT-AC86U, Is it safe? Increased lifespan?