So, in theory you can do this, but in practice there are a lot of ways it can go wrong too. If the supplies aren't perfectly matched (far closer than normal usage would require, so they probably aren't) they won't share the loads evenly, so you won't get as much extra headroom as you'd think, and if they're very badly unmatched they might drive power directly from one supply into another. Also, depending on their design they may also develop resonance/interference between them leading to, at best, very unclean power, and at worst, equipment-damaging surges. You might get away with it, if you're lucky, but i doubt anyone on here will be willing to say you will get away with it. I certainly wouldn't encourage it.