Both of these sit in the popular ~1,000Wh class, and on the spec sheet they look close. Independent bench testing is where they separate. Here is the measured picture, with every figure attributed to the lab that recorded it.
Real usable capacity
The Solar Lab measured the EcoFlow DELTA 3 Plus delivering 910 Wh of usable energy against its 1,024 Wh rating — 88.9%, the best in the 1kWh class. OutdoorGearLab measured the Anker SOLIX C1000 at 897 Wh usable of 1,056 Wh rated, or 85%. Close in absolute terms, but the DELTA 3 Plus returns a slightly higher share of what you paid for.
| Model | Rated Wh | Measured usable Wh | % delivered | Source |
|---|---|---|---|---|
| EcoFlow DELTA 3 Plus | 1,024 | 910 | 89% | The Solar Lab |
| Anker SOLIX C1000 | 1,056 | 897 | 85% | OutdoorGearLab |
Charging and UPS
Both recharge fast and both beat their own claims. The Solar Lab clocked the DELTA 3 Plus at 55 minutes on AC against a 56-minute claim, and OutdoorGearLab clocked the C1000 at 54 minutes against a 58-minute claim. Both held their loads as an uninterruptible supply in testing, with the DELTA 3 Plus measured at an 8ms switchover.
Where each one stumbles
The DELTA 3 Plus has a documented fan flaw. Under a 1,573W load The Solar Lab found the internals reached 138F while the fans would not spin up, which they called a glaring design flaw. T3 found the opposite symptom, with fans running constantly at idle. Its surge also measured only 2,600W against a 3,600W claim. The C1000’s main knock is noise: OutdoorGearLab called it one of the loudest units they tested at full load, and both Anker and OGL warn that its ultra-fast charging accelerates battery degradation.
The verdict
For efficiency and a slightly better real-world capacity, the DELTA 3 Plus edges it, if you can live with the fan behavior. If quiet-at-idle operation and expandability matter more, the C1000 is the safer pick, as long as you avoid habitual ultra-fast charging. Either way, size around the measured 85 to 89% usable figure, not the 1,024 or 1,056 Wh sticker. Full measured rankings are in our Honesty Index.
