first?

Total AC is 5?

Yeah, I suppose so. Wild, huh?

well its time for my turtal to have a 22 to ac without bunkering down in his shell

If you're a level 20 barbarian with a 20 in dex and a 24 in con (from level 20 class feature), then you'll have a flat 22 to AC. With this shield you can get a 27 in your armor class. Furthermore, if you take the fighting initiate feat and take the defense fighting style, you can get a 28, as a shield counts as armor.

Quote from EpicAlien454 >>

If you're a level 20 barbarian with a 20 in dex and a 24 in con (from level 20 class feature), then you'll have a flat 22 to AC. With this shield you can get a 27 in your armor class. Furthermore, if you take the fighting initiate feat and take the defense fighting style, you can get a 28, as a shield counts as armor.

 Step aside, Tarrasque, Barbarian is the true super tank. Also, if this barbarian has a Manual of Quickness of Action, he can have 24 dexterity, thus increasing his AC to 29.

You can theoretically get up to 32 AC if you have the Defender sword and put all 3 points into armor

Ring and Mantle of Protection to hit 34.

Add lycanthropy +1 for good meassure: 35 AC

Now this is an annoying villian.

Add mage armor 38 AC. Now who can hit you

Oh boy time to throw in defensive duelist feat to add plus 6 to your ac with a finesse weapon for 44 AC

As a spellcaster wearing the Robes of the Archmagi with 30 dex, this shield, and the shield spell cast as a reaction, you can have an AC of 35

is it an official rule that you can only benefit from one shield at a time?

Yes