DC-AC-DC is very inefficient (*). Better to allow a dialable DC output and then attach the shape plug required.
The smaller the battery the less its Wattage, the less you can tolerate any inefficiencies. The Powerhouse with 434Wh can only give 160W, so you can imagine even smaller given even less. The Powerhouse can be inefficient (* not in itself but the DC-AC in itself combined with the AC-DC of the PSU of the device) because it has a lot of Wattage.
Currently the biggest portable charger Anker which makes besides the Powerhouse has a 30W output, from 100Wh, so the 160W from 434Wh is proportionally higher.
I do think Anker can make more Wattage from less energy, but you hit a wall of usefulness that more powerful devices will receive proportionately less recharge % from less energy.