(resubmitted, previous one deleted by mods because of [Review] flair)

On another thread /u/Re-toast was asking how much % a 10000 mAh powerbank can charge a Surface Pro 7 via USB-C:
https://www.reddit.com/r/Surface/comments/dsd1h5/10000_mah_battery_pack_with_sp7
Coincidentally just some hours prior I ordered the Omars 10000 mAh 30W powerbank from Amazon for 15.82€ (available on Amazon US as well but more expensive with $28.89) and I decided to share my test results here. The Surface Laptop 3 has roughly the same battery capacity as the Pro 7 by the way.

First while my Surface Laptop 3 was turned on I checked how fast it is charging via a USB-C to USB-C connection (with the included cable). As a comparison I quickly checked my 60W USB-C charger (Baseus BS-EU910) and BatteryBar Pro indicated a charging speed of ~42W:
https://i.imgur.com/Uts7aCY.png

With the Omars Powerbank BatteryBar Pro indicated ~20W charging speed, however while idle the Laptop 3 takes around 4-5W, ergo it looks like the USB-PD is correctly negotiating 30W charging:
https://i.imgur.com/C342MHc.png

So I started the charging with the powerbank at 6.9% and after checking the charging speed I turned the machine off into hibernation at 7.6%.

After charging for 1 hour and 8 minutes the powerbank indicated it's empty. After turning the machine back on from hibernation it now had a charge of 67.5%:
https://i.imgur.com/bSz6dh9.png

Now let's calculate advertisement vs. reality:
Omars is advertising 10000 mAh @ 3.6V (36 Wh). Obviously there is some loss when converting to a different Voltage/Ampere, on the package it also says that a Samsung Galaxy S9 (13.48 Wh) can be charged 2.2 times -> 29.65 Wh. They also claim 2.4x iPhone X (10.35 Ah x 2.4 = 24.84 Ah) and 3.6x iPhone 8 (7 Ah x 3.6 = 25.2 Ah) so apparently the charging efficiency will depend on what Voltage/Ampere it outputs:
https://i.imgur.com/jnOmGnK.jpg

Transferring the highest advertised 29.65 Wh charging capacity to my Surface Laptop 3 with 48.14 Wh (see BatteryBar Pro screenshot, it's higher than the advertised 45.8 Wh capacity) I should have been able to charge it 61.59%.

In reality I was able to charge it from 6.9% to 67.5% = 60.6%. Considering the laptop was turned on for roughly the first 2 minutes of charging it's probably ~61% with it fully turned off the whole time. Regardless for my specific test I was able to charge 29.17 Wh, giving it around 81% charging efficiency.

All in all for 16€ I'm quite happy with the powerbank, it easily fits inside my Laptop sleeve pocket (113x80x22mm) and isn't too heavy with 334g. It's a bit bigger and heavier than other 10000 mAh powerbanks but all of those only include 18W charging, not 30W.
Size comparison of the powerbank vs. the Laptop 3:
https://i.imgur.com/a0m5lO6.jpg

tl;dr:
I was able to charge my Surface Laptop 3 ~61% (in 1 hour and 8 minutes) with the Omars 10000 mAh USB-C PD 30W powerbank (~81% charging efficiency, 29.17 Wh out of 36 Wh). There could be a 10000 mAh powerbank out there with higher or lower charging efficiency. However this is the only 10 Ah powerbank I found which 1) can be (30W) fast charged via USB-C and 2) output 30W instead of regular 18W.