Power banks: (W vs Wh) VS Security droids
 

I have an Anker 20000 mAh power bank, which at 5V output would be 100 Wh (20000/1000*5), at the usually-quoted "100W" limit for carry-on devices. Fine for in-town use, or car/train travel.
However, Anker UNhelpfully puts "(200W)" on the label beside the "20000 mAh" spec, which is true at 10V, and I'm sure one day I would be stopped by Security who just know "100W", so if I want to fly it would have to be left behind - don't want that.
Any experience here arguing electrical unit arithmetic with Security droids? Or should I just resign myself to purchasing a "flight" unit with 100 or less on the label, or no W/Wh on the label and perhaps I print my own "professional" sticker?

IATA rule is 100Wh.

Your 20,000mAh battery is at 3.7v, i.e. 74Wh

200W is specifying something completely different, probably that it has two ports that can negotiate 5A at 20v each with suitable hosts.

Understand that, but my worry is that at Security they have no idea of the distinction, and just say "100 is the limit, yours says 200, no go".

You run that risk. Some of the security people may have educated themselves. Others, not so much. If you get the wrong sort, you lose your power bank.

I also see various voltages cited above: 5V, 10V, 3,7V. Unless it's something that actually shows up on the nameplate, don't try calculating what the internals of the bank are. Odds are you'll just lose 99% of the security people in confusion and definitely lose the bank. It's 20,000mAh, 5V at the terminals. That's 100Wh, right on the line. What actually goes on inside the pack (buck-boost converters, etc.) is way above their heads.

And I'd suggest not making up your own sticker, because if they spot it (and the probably see a lot of these banks and know what looks odd), you may miss your flight as well. Buy the 100Wh, 100W power bank.

Or get one that expressly states energy in Wh directly on the label. This is becoming increasingly common.

Prolly the next step, off to bricks-and-mortar stores - online listings rarely/never show labels. Best Buy, Staples, Canada Computers, etc.

Indeed. I am sure that knowing the IV = Watts formula etc. and being able to correctly apply it, or rearrange it, is NOT part of an airport security person's training !!

Anything you want to take through security needs to state what security personnel have been told to allow.

And that's slightly wrong, too - because there's no issue with a 700W power bank/battery if you can find one, but they're actually after energy capacity. Which is charge (in amp-hours instead of coulombs) times nominal battery voltage (not written on the pack) equals energy in watt-hours.