If you buy a portable power station with a 1,000 watt-hour rating, you probably expect to get 1,000 watt hours of capacity but that simply isn't true and it isn't some marketing sleight of hand (at least most of the time.) Portable power stations state the actual capacity of the batteries such as 1,024 watt hours. When you plug in your fan or fridge, the energy in the battery must be converted to usable AC through an inverter that wastes some of the energy during the conversion. Depending on the design of the inverter in a portable power station, as well as the load put on it, the efficiency can vary dramatically. One final reason you'll never get 100 percent of what the label says is to preserve the battery. Lithium ion batteries can suffer damage when stored without any charge so each power station maker will cut off power well before it is empty to preserve battery longevity. Each vendor has different reserve levels, which also means your 1,024 watt hours of power is less than what you expect. So yes, it may seem like false advertising for a power station to state that you have 1,000 watt hours while only giving you 800 watt hours of usable capacity under a 200-watt AC load, but the reasons are technical, not marketing.