Can I bring a 30000 mAh power bank on board the aircraft?

From the IATA guidelines, all lithium batteries are subject to regulation, with specific rules depending on the type of device (portable electronic-device, medical device or spare battery).

A power banks is considered a spare battery (not a portable electronic device) and are restricted to carry-on luggage only (i.e. prohibited in checked luggage) and further restricted based on its capacity rating :

• Below 100Wh, the battery is allowed in carry on (with a maximum of 20 per passenger) without any operator approval needed.
• Between 100Wh and 160Wh, only two battery are allowed and the operator approval is needed.
• Above 160Wh is prohibited in passenger flights.

To avoid any issue, you should target a power bank with a capacity rating below the 100Wh threshold, even if that implies to take two of them.

If the energy capacity (in watt-hour) of the power bank is not specified in the product sheet, it can be deduced from the charge capacity (in ampere-hour or milliampere-hour) and the nominal voltage with the following formula : 1 Wh = 1V x 1Ah. But note that the electric charge of a power bank is not given relative to the output voltage (which may vary) but to the nominal voltage of the li-ion battery pack inside which is usually a bunch of 3.6V or 3.7V 18650 cells in series.

Your 30 000 mAh power bank would have a capacity around 110Wh (30 Ah x 3,6-3,7 V) depending on the cell type. Power banks designed for airplane carry are around 27 000 mAh to fit the 100Wh restriction and the capacity (usually 99,xWh) should be specified in the product sheet and written on the enclosure to avoid any issue.

The "Aukey" power bank PB-Y3 does not appear to have a Wh rating marked on the outside of the case, based on studying a Russian review video.

The typical airline 100Wh limit could be considered to be exceeded then, by the airport security personnel since 3.7V * 30,000 = 111Wh. I have seen them take power banks away from people (in Asia- US security seems to be more lax in that regard).

For what it's worth (from a teardown video) the internals contain 3 pyramidal cells marked 3.7V 10000mAh so the rating is as honest as the Chinese battery maker (BTC, apparently). I suspect it's somewhat- "optimistic" in this case, but that's just my opinion (based on seeing a lot of other dubious claims- and a case of BTC batteries I was gifted because they didn't meet specifications).

Personally I would get a Huawei or Xiaomi 20,000mAh power bank rather than this one, if it was available off the shelf. They're brand-name cell phone makers (so they definitely know batteries) and have good reputations for quality and safety. I have hiked as long as 13 hours using an iPhoneX running mapping applications using the phone and an alleged 11,000mAh power bank (low power mode on the phone much of the time). There was plenty of juice left in the power bank if I got a chance to charge it mostly. It takes quite some time (as much as 9 or 10 hours) to charge some of the power banks, and you probably want them close by while charging.

Keep in mind, the higher capacity power banks are significantly heavier and you have to lug all that weight around or nothing. There are often opportunities to charge your phone at restaurants, cafes, workplaces etc. and unless you're doing a lot of video work or obsessively playing with your phone you may not use that much juice. However, mapping applications do tend to use a lot of power- and, at least on my phone, they keep the screen on consuming even more power.

Safety wise, keep in mind that 111Wh is 400kJ of energy. A .45 ACP bullet carries 0.5 to 0.8kJ. A stick of dynamite is about 1000kJ.

Edit: For what it's worth, I just bought a Huawei 20,000mAh power bank myself, model CP22QC (CNY269) and it is clearly marked on the unit (where anyone inspecting can read it) as 68.97Wh, well under the 100Wh limit, so they are assuming an average lithium ion battery voltage over the discharge curve of 3.4485VDC. Note that there is a common (rather optimistic) misconception that the mAh ratings quoted apply to the output. The output will be less by the voltage ratio and even less than that because the DC-DC conversion process is not 100% efficient. At 85% efficiency you might get 11,500mAh from the output.

Note & tl;dr: I'm certainly not endorsing any particular brand, but I would suggest buying a major world-wide cell phone brand.