powerschute is proprietary software, I avoid 'non free software' like hell, sorry, can't trust it.
In any case, with apcupsd you can have a client-server config and monitor multiple ups as well.
I'm not aware of any KVM "guest addition" that can do what you (we) need in the unfortunate circumstance we have to virtualize M$-OSs.
Fortunatly, considering the fact that KVM is Free Software, everyone can contribute and/or support it's development.
Speaking generally (not of course against you or your question), OMHO Free software is not "gratis", "no price" software, instead everyone has the moral duty to give money/help to FOSS projects and should consider that, in any case, donating now will save a lot of money later (compared to proprietary software), and Free software gives you much more (freedom) than a comparable proprietary product.
So my idea is that would be nice if Proxmox people could manage one or more "bounty" projects where Proxmox (or other free software) users can promise (and anticipate) a certain amount of money for the completion of a specific project that is outside the roadmap of Proxmox team, like this one. Me (being just a hobbist employed in a SME where Proxmox and other FOSS is used with a moral attitude I don't agree with) could donate 100 euros.
Just an idea...