The idea behind a power bank is that when you are out-and-about, you can recharge your gadgets without needing a wall socket! The overwhelming majority of power banks are limited to USB devices like a smartphone, although there are some power banks like the Maxoak K2, which can also output 30W (12V/2.5A) and 60W (20V/5A) to charge a laptop!
The Maxoak K2 is a behemoth of a powerhouse, way larger (20.7cm long, 13.5cm wide and 3.2cm thick) than your average power bank but, then again, it would be since the Maxoak K2 can store over 30 hours of power. The K2 weighs 1.2 kg too, which is even heavier than some laptops.
The aluminium body of the Maxoak K2 wraps around the front, back and sides of the power bank, while the bottom and top end panels are capped with hard plastic that is rounded off at the corners. Across the sides of the Maxoak K2 powerbank there are glossy bronze plastic strips with printed information.
The top panel contains the functionality, including battery led indicators, DC input, power button, a 20V/5A DC output and a 12V/2.5A DC output. The power button also activates the battery led indicator. The K2 power bank has been programmed to power off automatically after 30 seconds of current load not being detected.
There is also four USB output ports, two of which can output 2.1A, while the other two USB ports can output 1A, which is ideal for charging 5V USB powered devices like a smartphone or, even smaller power banks. The K2 power bank is able to recharge 16 times over, a 4000mAh smartphone and 2 times over, a 60W laptop.
The K2 power bank has a 1000 cycle life, which means you will be able to completely charge it and discharge it 1000 times without losing charge capacity. After 1000 complete charges/discharges though, the K2 power bank will start experiencing issues holding charge, which is an issue all power banks/rechargeable batteries eventually experience.
With 1000 complete charges/discharges, you are probably looking at 3 years, although you can easily extend this number by simply not letting the battery go flat. If you only let the Maxoak K2 battery discharge to 50% and then charge it back up to 100%, it only counts as a 1/2 cycle.
The Maxoak K2 power bank supports simultaneous charging/discharging, which means you can charge devices and recharge the K2 power bank, all at the same without having to wait for the power bank to fully recharge.
In order to recharge the Maxoak K2 50000mAh battery, it requires a 1.5A input within 100V and 240V voltage range. The United Kingdom (UK) operates on a 230V supply voltage, while other places like North America and Hong Kong operate on a 110V and 220V supply voltage respectively.
You won't be able to use an AC 100-240V to DC 12V/1.5A power adapter to recharge the K2 power bank. The included power brink though, it's effectively a 42-watt fast charger, which can recharge the K2 in 7 hours. With this much power going into, the K2 power bank has not problems outputting its total 120-watt power capacity from the DC outputs and USB outputs at the same time.
The power supply that is included with the Maxoak K2  is a branded power brick AC/DC adapter made by KAYO Maxtar (Model Number: XVE-1680250). KAYO Maxtar seem to be a subsidiary company of Maxoak.
The KAYO Maxtar AC power adapter has the same footprint as a regular laptop power adapter and it's also limited to 1.5A, although you won't be able to directly connect the KAYO Maxtar power adapter to a laptop without the K2 power bank. The reason being, the KAYO Maxtar power adapter output has been customized to 16.8V at 2.5A, which is lower output than most laptop charger bricks.
Speaking of laptops, the Maxoak K2 power bank comes with 14 male jack connectors to fit a range of laptop charging ports (Apple laptops not supported). All the jack connectors are dual-sided and have a 5.5 x 2.1mm DC female jack on the rear to plug in the included DC male to male 20 AWG cable, which is rated for a maximum working voltage up to 125V.
The dimensions of the jack connectors are as follows: 6.0 x 1.4mm (Fujitsu), 6.5 x 4.4mm (Sony), 5.5 x 2.5mm (Acer, Asus, IBM, Dell, HP/Compaq, Fujitsu, Toshiba and NEC), 5.5  x 1.7mm (Acer), 4.8 x 1.7mm (HP), 5.0 x 1.0mm (Samsung), 7.4 x 0.6mm (Dell), 7.4 x 5.0mm (HP), 7.4 x 0.6mm (Dell), 7.4 x 5.0mm (Dell), 7.9 x 0.9mm (IBM), 7.9/5.5mm (Lenovo), 3.0 x 1.1mm (Samsung), 4.5 x 3.0mm (HP), 4.5 x 3.0mm (Dell), 4.0 x 1.35mm (Asus), ASUS and 4.0 x 1.7mm (Lenovo). The 4.5 x 3.0mm connector does not work with the Dell XPS 12.
There is also a Lenovo square connector for the ThinkPad Yoga S1, ThinkPad Helix and ThinkPad T431s laptops. This Lenovo square tip connector will not fit any other Lenovo laptop, including the Yoga 3 14, Yoga 900 (20V 3.21A), Yoga 700S, Yoga 3 11, Yoga 13 and One Mix 4 Yoga.
If the included connectors don't fit your laptop, you will need to buy a jack connector in order to be able to use the Maxoak K2 power bank. The included jack connectors will not fit a Surface Pro 3 or Surface Pro 4 since these two laptops require a 5.5mm x 2.1mm DC male connector.
While talking about the Surface Pro 3 and 4 laptops, it's worth pointing out that the Surface Pro 3 and Pro 4 have a stock voltage input of 12V and 15V respectively. That said,  the Surface Pro 3 will accept any voltage supply between 11V and 16V, while the Surface Pro 4 can still operate from a 12V power supply, although charging will be naturally slower. The 20V outlet is good for laptops with voltage ranging from 18.5 volts to 20.5 volts. This includes the HP Envy 360 Convertible laptops, which have a 19.5 volt rating.
The KAYO Maxtar power adapter internal circuit has a class 2 rating, just like most laptop chargers; hence the KAYO Maxtar power adapter integrates double insulation that prevents electric shock and fire. The KAYO Maxtar power adapter features at one side a figure 8 female port to plug in the included detachable power cord, as well as a non-detachable cable with a DC barrel plug connector (4.0mm x 1.35mm) at the other end.
As far as safety, The Maxoak K2 power bank comes with a safety warning to remind users to use the correct voltage for the device they intend to power/recharge because you may well damage the device if it doesn't have over-voltage protection. Most devices these days though, have intelligent circuitry that detects voltage automatically to prevent any damage.
Being a 185 watt hours (Wh) power bank, the K2 powerbank is well above the 100Wh passenger airline threshold, meaning you won't be able to take the Maxoak K2 on a plane, not even in checked baggage.
Other accessories included with the K2 power bank are a USB-A to micro USB cable and a neoprene pouch to carry or safely store the Maxoak K2 power bank. Being neoprene (rubber), the pouch provides moderate shock-absorbing protection against bumps.
The neoprene pouch has two pocket compartments. One for the powerbank, which has dual zippers, while the second (front pocket) has a single zipper. The zippers have stocky hard plastic pull tabs and a reverse coil design, which provides some water resistance, although not waterproof like neoprene. You can buy the Maxoak K2 laptop power bank on Amazon.