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It’s compact and looks built to take a few knocks, but the WAI PPS-400 has a limited range of ports, crammed into two small panels. Despite a surprisingly high battery capacity and good discharge efficiency, it’s rather slow to charge and isn’t especially confidence-inspiring to use. Overall, this is a cheap way to buy a mains power bank with a decent capacity, but I’d rather spend a little more on something that feels more dependable.


  • Light and compact for this capacity
  • Range of charging options
  • Good output efficiency at load


  • Crowded control panel
  • Not the best port selection
  • Unreliable at higher loads

Key Features

  • A small-medium power bankThis compact power bank packs a strong 426 watt-hour battery – enough to power a computer for a few hours
  • A range of portsPower mains and USB devices through a range of ports – but not the most comprehensive we’ve seen.


WAI is best known for its range of car accessories, but its PPS-400 is an all-purpose portable power bank.

It’s compact and light compared to the competition, yet it packs in a 426Wh battery, giving it a bit more oomph than you might expect for its size.

The port selection includes two USB-A and two AC sockets, with the latter capable of supplying 400W between them – that’s a cut above entry-level devices, making this a compelling power bank for the money. However, I found it to be unreliable at higher loads, so it may well be worth spending a little bit more elsewhere.

Design and features

  • Light, compact and rugged
  • Cramped and unimpressive port selection
  • Very basic display

While many portable power supplies look more like a stereo than a battery, the WAI PPS-400 looks like something a mechanic might use to start your car. Indeed, it’s part of the company’s new EV range, which also includes a selection of EV charging cables. I’m not entirely clear how it fits in – it’s far short of the power you’d need to top up an electric vehicle’s battery.

The PPS-400 may look drab, but it’s impressively compact. It’s slightly narrower than a loaf of bread, and weighs only 3.7kg – the same as Anker’s PowerHouse 521, which has only just over half as much battery capacity. On top there’s a retractable handle, but the four long sides are otherwise featureless aluminium – all the important bits are crammed into the two small, square ends.

WAI PPS-400 side view with handle
Image Credit (Trusted Reviews)

That’s not great. The business end combines AC and solar inputs, a lamp, display, two USB-A ports and two 12V DC ports, alongside switches for the lamp, DC and AC ports. Add in fresh air vents and it’s a cramped space with a fairly arbitrary layout.

The light is bright and directional, which is great for finding your way, but less so for reading in a tent at night. The switches operate with a pleasant click, and the plastics seem strong.

WAI PPS-400 power inputs and USB outputs.
Image Credit (Trusted Reviews)

At the back end are two AC ports, plus fans for active cooling.

WAI PPS-400 AC outlets.
Image Credit (Trusted Reviews)

Here, the small panel poses another problem: the ports are arranged horizontally and orientated 180 degrees from each other. Some top-heavy power adaptors won’t fit without blocking the second port, while regular power plugs are close to the edge of the device.

This means cables project from the side, with little ability to flex if they’re knocked. In combination with the loose-fitting multi-region sockets, it’s too easy to knock a plug loose.

WAI PPS-400 AC outlets with plug connected.
Image Credit (Trusted Reviews)

The WAI PPS-400 has a very basic display, showing only the battery charge percentage. It’s off unless you turn on the DC or AC circuits, and doesn’t provide any indication of incoming or outgoing power, or how long the battery will take to charge or drain.

WAI PPS-400 charge display.
Image Credit (Trusted Reviews)

It’s a shame WAI hasn’t found room for any USB-C ports, or a car output. The USB ports can provide 15W each, while the DC outputs are good for a combined 120W maximum.


  • Charge from mains, car or the sun
  • Maximum 70W input
  • Charges slowly, but can charge and provide power

This isn’t the fastest charging power bank, but it is fairly flexible. Connected to a mains input it’ll charge at about 55 watts, meaning it should need around eight hours to reach full charge. Alternatively, you can use the supplied cable to charge from a car power supply at a maximum 70W, meaning you could be fully recharged after around six hours of driving. A final option lets you connect up to 70W of solar power, but this is limited to a maximum 18V input. The PPS-400 doesn’t come with panels and I didn’t have suitable ones, so I couldn’t test this function.

WAI’s manual says that this power bank’s charge light turns from red to green when it’s fully charged. It also says that the display will show 100% charge when the battery reaches 90%. In practice it wasn’t clear when it was fully charged – the charge light never turned green, and even after more than 12 hours the PPS-400 was still consuming around 6W with all its circuits off.

After fully depleting it again, I watched the figures more closely. The display reported 44% charge after my meter reported it had drawn only 87Wh – about a fifth of the battery capacity. When the display first reached 100%, my meter reported only 275Wh (65%) consumed, and that the power bank was still drawing 60W. After around 13 hours it had consumed 507Wh, but still didn’t quite seem full.

This vague and seemingly inaccurate capacity reporting seems a bit unusual by today’s standards. I couldn’t be sure that the battery was fully charged but, even assuming it was, my measurements suggest a charge efficiency of 84%, which is a little low. I should also mention that the cooling fans cut in and out during charging, and while they’re not loud, their small diameter means they’re a bit harsh.

The WAI PPS-400 is equipped with a bypass circuit, meaning that when it’s connected to the mains it can supply mains power without first having to convert it to direct current and back. This lets it power mains devices without slowing down charging. Its AC input is rated at three amps, meaning that in theory it could provide around 650W to plugged in devices while charging the battery. I tested it with my microwave on its lowest power setting, which demands between 60-650W, and it coped fine.

The bypass circuit means the PPS-400 needs to switch over to battery power if there’s a blackout. WAI says it can do this in less than 10 milliseconds, and it was certainly fast enough to switch without causing my office equipment any problems. At an indicated 20% the display starts flashing to warn you that the battery is getting low, and at 0% it starts a very loud intermittent beep. While that’s good if you want time to shut down your devices, this phase lasted for 35 minutes in my low-load test, and there’s no button to silence it.


  • Unreliable power output
  • Good discharge efficiency on heavy loads

In theory, this power supply’s moderate capacity makes it a good choice for light backup duties in the home. For example, it could potentially power my internet router and network storage (NAS) drive for about seven or eight hours – ideal for riding out a significant blackout. I tested it by connecting up an air purifier, drawing around 32W. It lasted for eight hours, supplying a total of 240Wh according to my power meter.

Assuming the battery began with a full charge, that’s a low discharge efficiency of 56%. That’s not unusual for light-load testing, however, where consumption by the power bank’s own AC inverter has quite an impact over several hours.

WAI PPS-400 torch turned on.
Image Credit (Trusted Reviews)

I tested the PPS-400 with a more demanding setup drawing around 220W, which is well within the range of its stated 400W AC output. It started off quite comfortably, with the fans occasionally kicking in, before it cut out after about ten minutes. It reset automatically and continued for a couple of minutes before the fans cut in again, and about 10 seconds later it reset. I watched it repeat this cycle a few times, keeping a close eye on the maximum power demand as reported by my power meter – it didn’t exceed 220W.

I reconfigured the test to reduce the demand to 190W, which proved stable. If I tried increasing it back to 220W the PPS-400 would fall over within just a couple of minutes.

Tested from full to empty with a 190W load, the WAI PPS-400 lasted about an hour and three quarters, supplying a total of 328Wh. That equates to a much more impressive discharge efficiency of 77%. Unfortunately, even using this the best round-trip efficiency (charge and discharge) worked out at 65% – meaning about a third of the electricity used to charge it was lost.

I repeated my low-power microwave test with the PPS-400 operating on battery power. It coped for a few seconds, but the moment the power demand spiked towards the 650W maximum it shut down. This is safe and quite reasonable, bearing in mind I was testing it well beyond its stated 400W output power.

While more expensive power supplies use LFP batteries of the type found in electric cars, the WAI PPS-400 uses standard lithium-ion (Li-ion) cells, which have a shorter working life of around 800 cycles, compared to typically 3,000 for LFP. Calculated based on an 80% charge, this power bank might store about 273kWh over its lifetime. That gives an overall price per kilowatt hour of £1.10, around three times what you might expect from more durable cells.

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Should you buy it?

You want high capacity at a low price: This provides a good battery capacity for the money

You need more power output: This battery station wasn’t fully reliable in my tests

Final Thoughts

On paper this ought to be a decent power bank, but in tests the WAI PPS-400 was disappointing. It was slow and comparatively inefficient to charge, and its basic display seemed approximate. More importantly, it wasn’t stable when supplying well within its rated power, which didn’t fill me with confidence about its quality.

Based on my experience, it might not prove reliable in situations when it should be. It might be good value for use with low loads, but I’d be inclined to pay more for something more robust, such as the Bluetti AC60 or, if you need a lot more power, the Dabbsson DBS2300.

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We test every battery station we review thoroughly over an extended period of time. We use standard tests to compare features properly. We’ll always tell you what we find. We never, ever, accept money to review a product.

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We test with a variety of devices to see how long the battery will last.

We test different charging methods to see how quickly the battery can be topped up.


Is this suitable for powering a CPAP device?

On paper, the WAI PPS-400 should be suitable, but my experience with it resetting means I can’t recommend it for critical medical applications.

How portable is this power bank?

It’s extremely portable. It’s lightweight given its battery capacity, and compact enough to sneak into a full car boot.

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