You’d be surprised. A little window rattler AC could be powered by such a setup - ie I have a 1.6kw cooling A/C with an input rating of 490W, I’ve measured it to be around that. That will cool a bedroom somewhat. The issue will be the surge power when the compressor kicks in, so maybe add 50%.
SD-WAN includes that but it is not its sole purpose, although I agree most vendors will say that’s what you want. WAN/Link Aggregation, Multilink Aggregation, Link Load Balancing, Equal Cost Multipath, WAN Virtualisation, etc are ways to bundle multiple links together.
In WIFI terms, it’s called channel bonding, it was proprietary and various vendors had their own implementations, see “Super G”.