High Speed Serial Communications?
In the Youtube video “How to connect your Plus 4 to a BBS,” the host points out to one thing that no other 8Bit Commodore has: an 8551 UART (Universal Asynchronous Receive & Transmit Serial Chip), which is sometimes replaced with the MOS Version 6551 ACIA (Advanced Complex Interface Adaptor). The 8551 is the first generation UART chip, allowing 19.2K bit rate with simultaneous Transmit and Receive; which the 6551 ACIA does not have or can not do. The 6551, like all the other MOS Interface Adaptor chips can do serial communications with software assistance, where the 8551 does serial communications directly without the need of software. Connected to the User Port of the Plus 4, it makes the User Port as a true RS232 Serial Port. The User Port on other Commodore 8Bit systems are not true RS232 serial Ports.
 
https://www.youtube.com/watch?v=daoAllAv9qo
 
The 8551 UART is the serial chip used on the original IBM PCs’ serial Cards before the 16551 came out a couple years later. The 16551 is pin compatible to the 8551 and has faster bit rates with better error correction, and are used in later PCs after the ‘386 and used in most PCs today that still uses Serial Ports, which are many used in industrial settings.
 
Up to this point, the Commodore 8Bit systems used various Interface Adaptor Chips where the CPU fetches or sends 8bit parallel data bytes from/to the Adaptor Chip and send it to a buffer before it can be placed elsewhere in memory. The 8851 UART gets the Serial Data, converts it to an 8Bit byte and sends it to a programmed buffer where the CPU gets the data from the buffer; saving processor steps in data transferring within the machine’s architecture.
 
The Plus 4 also has 2 6529 SPI Chips used the I/O of the machine like the other various Interface Adaptor chips were used on other Commodore machines: cassette, disk drive, keyboard, joystick; the paddle I/O is handled by the TED Chip like it is done on the Vic chip on the Vic20.
 
Because of this UART inside the Plus 4, it can use a 56K Modem and can be connected to faster devices than on the C64/C128, Vic20, Commodore PET or other 8Bit Commodore systems, which at best can connect to a  9600/1.44 Baud Modem or slower serial devices.  
 
As much hardware the C16 shares with the Plus 4, it does not share the UART and therefore does not have a USER port and is the only 8Bit Commodore System that does not have a User Port. The C16 can be upgraded to 64K and be given the Plus 4 Software as to operate software wise like a Plus 4 but without its User port, it can not be connected modems and other serial devices.  
 
Links:
Adding Plus4 software to a C16: https://www.youtube.com/watch?v=jA3R7_r_6TQ
 
 

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Switching Between NTSC and PAL on a Plus 4?
 
In most cases, one needs the video processing chips and some clock frequency circuitry for running NTSC or PAL video. The Vic20 uses the 6560 for NTSC and 6561 for PAL; The C64 uses 6567/6566/8562/8564 for NTSC, and 6569/8565/8566 for PAL. The Plus4/Commodore 16 however uses one chip for both, the 7360/8360, aka TED Chip. (Text Editor Chip), as envisioned by Jack Tremiel in order to produce a low cost small business and higher education student system. But at this some, the newly formed Commodore Board of Directors fired Jack Tremiel as CEO of Commodore and not knowing what to do with the Plus4, sold  it at the same price as the Commodore 64 (around $199), and created the C16 and sold it at the same price as the Vic20’s lowest price years before ($99). This marketing strategy basically destroyed the Plus4 as Jack’s original intention was sell the Plus4 for around $99 to $150.
 
Since the Plus4 and C16 uses 1 chip for either NTSC or PAL makes it capable of switching to either/or with the right hardware hack. Adrian’s Video uses a couple added parts to switch the clock frequencies and ROM to obtain NTSC or PAL at a press of a button. One does not have to buy a separate TED Chip for PAL or NTSC. The hardest part of this hack is getting a ROM for the TED Kernel that has both NTSC and PAL routines. An Arduino is used to go the switching of the clock and ROM Sections to run NTSC or PAL.
 
The video for this is very short and direct as to how to do it.
 
Video Link: NTSC or PAL https://www.youtube.com/watch?v=RwLsFSg0FdU
 

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[b]6510 On A Plus4/C16? [?/b]
 
The Plus4 and C16 use a variant of the 6502 CPU, the 7501/8501. This processors allows bank switching to happen at a faster rate and be able to access RAM and ROM in the same locations at the same time, giving the Plus4 63K of usable memory for direct use by BASIC. But like all things old, these CPUs are no longer being made and many C16s and Plus4s are showing up with dead CPUs. The question that lies “Is there a replacement for the 7501/8501?”
 
With a bit of hardware hacking, there is. One can take the 6510 from a Commodore 64 and with a socket adapter, replace a 7501/8501. This hack seems to work because it seems that the 6510 and the 7501/8501 are very similar but with a few pins switched around. the adaptor switches the pins about and makes a 6510 work as a 7501/8501.
 
The problem is, there is a limited number of 6510 CPUs out there. I know that years ago somebody was working on a 6502 to 6510 adaptor, but nothing was heard from it for a long time. If one could get a 6502 to run as a 6510, then they can take one step further and make  6502 to 7502/8502 adaptor.
 
Video Link: 6510 Replacement? https://www.youtube.com/watch?v=xRNb7NjgWTo

Getting a 5V Cellphone Charger (2 or more amps) should be more than enough to turn on the Plus4/C16, though with the 9VAC missing would "kill" the cassette and User Port. In actuality, the 9VAC is converted to 12VDC and is used to run the Cassette Drive Motor and without it, the cassette would not work. As for the User Port, there is a 9VAC pins to power any devices connected to it. In the least you be able to turn on the machine and test out the BASIC on the screen.
 
I seen a video (I think Adrian's Digital Basement) that said that 90% of all Plus4/C16 failures (Black Screen when turned on) is a dead CPU. Rarely is it the TED Chip though that can fail too. Getting a 7501/8501 CPU for the Plus4/C16 can be difficult or expensive. You could use the 6510 to 7501 hack to repair the dead CPU.