Hacking DSLR battery to power camera from power supply
There are many ways this could "go wrong".


It almost certainly violates the terms of the warranty on the camera.
The voltage of the charger may be out of tolerance for the camera. (Obviously, the charger voltage must be significantly higher than the terminal voltage of the battery in order to accomplish its function.)
The charger is designed to safely charge a specific battery. The load of the camera will almost certainly confuse the charger's internal logic.
DSLRs are notorious for drawing a huge spike of current when a picture is taken. The charger may not be capable of supplying this current. The terminal voltage will sag, possibly messing up the camera's logic.


I have built external power supplies for DSLRs (for aerial photography). Trust me, they are not just "dumb power supplies". Tight voltage regulation combined with high peak current capability makes them non-trivial to design.