How much loss is there for a converter? I always thought that for the most part they were pretty efficient. Unless you've measured and found a difference, you might be trying to solve an issue that isn't a huge one.

I've been very happy with my Cyberpower setup, and the smaller one is powering my router and monitors. It's still 650VA, so will roughly match the time the larger one would keep my computer alive. I'm not running a server though, so it might still be low for you, but 12V 5A doesn't seem like a large pull.