Will Autel MK808S get more details on DTC C1391Brake Accumulator pressure?

My questions tonight...
1) Should I expect a new scan tool 'Read', or just shut down like my cheap OBD2 reader does? (I just ordered an Autel MK808S $383 on Amazon to arrive in 2 days (Black Friday sale saved $96 )
2) Would this MK808S be able to tell which component is causing the inability to hold pressure adequately between either the Brake Accumulator & Pump Assy(lower unit I think), or the Brake Booster Assy (upper unit I think)?
3) I tried ChapmanF's suggetion (ChapmanF, thank you for all your detailed info on the codes. etc!) to use my mechanics stethoscope to listen to the pump, the accumulator next to the pump, and the Brake Booster Assy above for a hissing sound of a leak in the 9-10 between pump cycles. I heard no sounds at all, other than the pump when it ran. My preliminary Toyota parts price check says each of these units are +/- $600.
4) If only one of the units is causing either a pressure leak, or the pump is failing* to provide enough pressure, is it prudent to replace the other one because it has a likelihood of failure sooner rather than later??
5) *Actually, since the pump seems to add enough pressure to bring it into spec, in just 1to1.5 secs, would that imply it was doing its job well, but pressure escapes and starts the pump again. I forget when actually driving the car and listening, but the does run much longer cycles when the car is being driven.
6) I guess I could clear the codes and see how long they take to return, But I think it may be better to leave the historical info in the system to see what the new scan tool on Saturday might be able to tell me.

Reading on Prius Chat for hours on this issue last night and today, I learned it was likely the brake fluid pressure not being held in the brake accumulator. I did Jump the #4 CG and #13TC pins in the OBD plug and got:
((!)) (! w/ circle and parens) Brake System Warning light: code 69 (DTC C1391).
ABS warning light: code 42 (means go see codes at ((!)) )
Skid Indicator: code 45 (means go see codes at ((!)) )
Airbag, EPS, Tire!, (!), Chk Eng. Light, all blinking continuously.
'Brake' and 'Battery' icons on solid the entire time, no blinking.

My cheapie TopTak TP-110CAN ODB2 reader would not work. It would power on as normal, but every time I hit 'Read', it just turned off*. It acted the same way when tried in our 2017 KIA, but it worked as normal on my 1999 GMC truck. I pulled the old battery (8.0V) put a relatively fresh (9.33V) 9 volt battery in the reader and got the same result. I watched a video on pulling the pins out of the OBD2 Molex connector to make sure they were not loose. Looked closely and probed the pins lightly, they did not seem loose, so I did not pull the pins.


How it started:
My wife's Gen 3 2013 Prius Plug: About a week ago, she called saying at about 40mph she pressed on the brake pedal and only felt 5-10% of the braking power, and the pedal went down much further than normal. She made her way to the side of the road and drove on the shoulder at 15-20 mph to get home. The next day, I did a short test drive and maybe the pedal travel was lower than normal still (but I normally don't drive it, so not sure). Getting in the car, pressing start button twice (w/o brake pedal) to be in IG-On, there is the tell-tale brake pump motor runs 1-1.5 seconds, off for 9-10 secs, repeat until turned off.

Thanks for any insights on scanning and troubleshooting going forward.
Oh, and a very Happy Thanksgiving to all!
Dave