The Bluesea 1045 can do 2.4A per USB port, so it is indeed a 12W charger. It can do a total of 4.8A for both ports.
If you want to stick with this form factor there are other options that can provide higher current. AFAIK the iPad 12.9 Pro comes with a 20W USB-C charger.
The battery is probably around 40 W-hr and I've read that it will peak at 35 watts charging so would basically hit its maximum rate with a 30W or larger charger. So an 18W charger would probably keep an active iPad with its screen on at it's starting charge or allow it to slowly charge.
The 18W charger that ships with iPad Pro really isn't taking full advantage of the speeds the tablet is able to achieve.
wccftech.com
This one has one QC3.0 (18W using a USB A) and QC4.0 (it'll do 36W on a USB-C typically in a 12V car).
High output combination USB QC3.0 and USB Type-C QC4.0 charger. Powerful USB Type-C is capable of 36W output with 12V DC input, and up to 60W with 20V DC input. Support for multiple fast charging protocols. Fits standard 1-1/8" diameter hole. Ideal for charging smartphones, tablets, and laptops.
powerwerx.com
Or this one, which is a pair of QC3.0 (18W) ports.
Dual QC3.0 USB device charger with support for multiple fast charging protocols. Fits standard 1-1/8" diameter hole. Maximum output of 18W per USB QC3.0. Ideal for charging smartphones and tablets.
powerwerx.com
One thing I've noticed is that Apple is strict about the charger being correctly designed, in particular in how the power delivery negotiation is done. If the charger is done in a non-standard way Apple devices are quick to default to a safe configuration.
All devices may do this, I have a Motorola phone from a few years ago that is only used for amateur radio stuff and it won't take more than 7.5W from one charger I have even though it's supposed to be capable of 30W. I use it as a dumb 5V supply but it's all but useless to anything modern. Looking inside it there's a USB controller chip marked T.I. but my best guess is it's counterfeit and so the phone assumes it's a plain USB 2.0 port.
Now that said Bluesea in my experience should not suffer from that problem, so as was said you just need a higher power USB adapter.