You might consider the 18 TB for $200 deal from Best Buy as well for more density, though this deal is better on a terabyte-per-dollar basis.
I haven’t bought Seagate externals to shuck but I’ve bought a lot of WDs over the years for my Unraid box and I’ve had no issues with them.
If the power supply is modular, check both ends of the power cable to make sure it’s seated fully. Also check both ends of the data cable. If it worked with the old power supply and stopped working after only changing the power supply, that suggests a cable is not plugged in correctly.
Also, if it is a modular power supply, are you using only cables that came with the new one? Cables from different models are not necessarily compatible with each other.
Other people have addressed why 64-bit is still fine, but I just want to say that “x86” and “x64” are not two different architectures the way that you’re presenting them. We still use the x86 architecture, it’s just that x86-64, or AMD64, or whatever you want to call it, is a 64-bit extension of that architecture.
And this isn’t the first time that happened; the original 8086 was a 16-bit processor, as was the 286. The 386, however, was a 32-bit processor with backward compatibility for the 16-bit software built for the 16-bit x86 CPUs.
The 386 came out in 1985, so there’s actually a 14 year gap, though actually actually an 18 year gap because a 64-bit x86 processor didn’t actually hit the market until 2003. And then there was a 7-year gap between 16 and 32-bit x86.
But ultimately as other people have said the answer is that we don’t need to go beyond 64-bit right now, and the reason there was such a short gap between 16 and 32-bit processors was because the limitations of a 16-bit architecture became practical obstacles to progress faster than they did for 32-bit, and it’s going to be much longer than that for 64-bit because the address space has grown exponentially, not linearly.