I am very certain there's a short occurring here somewhere, but exactly where I cannot ascertain. These are not BSOD crashes, they are power failures causing immediate system shutdown/reboots. Since you've changed the network adapter, we can rule out your PC being the cause.
I recommend doing some network changes here. Hook the printer directly to the PC and see if print jobs will cause it to short. Try changing the port used on the router that the PC is directly hooked too. Try hooking another PC up to the router directly while the printer is on the network via the router.
Basically you want to try and perform a number of permutations of your network design to see if the printer is the cause of the short or the router. Of course, you can always just get replacements of each, but that's a bit of a caveman way of doing things and can get costly.