The concept of a "power splitter" is fundamentally mistaken for devices using voltage mode supplies. You need to concentrate instead on the specific supply requirements of your motor. If you really want to do this, get a mains supply which meets the motor's needs, and then use a DC switching regulator to drop that down to what the pi needs, making sure that the first motor-voltage output is high enough that the pi regulator's input requirement will be met even when the motor loads the supply. Using distinct mains supplies would typically be the simplest...

Please edit the question to include the electrical specifications of your servomotor or its driver board, if that is external to the motor itself.

@mguima until we know the nature of the asker's motor, it is impossible for anyone to meaningfully help them. And that is not just a practical necessity, the requirement to include such information happens to be a fundamental rule of this site.

Matthew: It will greatly help people help you if you provide web links to anything you are using . The term "servo" can cover several quite different motor types and power and voltage and drive requirements for what you are probably using vary. Please provide brand & model of your servo motor and a web link to a data sheet (or a technical description if data sheet not available). A web link to a Pi Zero datasheet would also do no harm. || Note that what Chris says is valid - to get a good answer that works it is necessary to be sure of what the real requirement is.

We don't yet know that this is an "RC hobby servo" the term "servomotor" tends to mean the much more power hungry and capable industrial sort of device. Until the asker says what they have, anything posted is guesswork, and that's not what this site is for.

@ChrisStratton I agree largely with what you say. I'm trying to steer the conversation in a way that a new user will feel comfortable with. Even very good advice can be fairly offputting when new to how things work. It's still needed but ... . I was about to add a "You need to ..." comment.

@ChrisStratton and Russel, 99,999% chances that OP has a blue 9G servo. I edited my answer, because of course the circuit needed to isolate the SBC and the motor would be a lot complicated to OP build.

@mguima has provided a useful link in his answer. BUT do note Chris Stratton's comments also. Any motor tends to make electrical "noise" which a microcontroller is very sensitive to. Also, usually the power needs of a motor exceed that which what can sensibly be fed from a Pi header directly. Finally, the voltage needs to be correct and may not match the Pi supply. Overall, when starting off, supplying the servo from a separate supply, batteries or other is a safe move. Grounds of Pi supply and servo supply MUST be connected. The servo control lead can usually be driven directly by the Pi.

@Matthew, I like your little cute yellow cubes very much. I would give 5 stars (Top 1%) to your question. I guess, from your concise question and the use of the words "transistor chip", "splitting power", "servo motor" that it is very likely that you are like me, a hobbyist. You remind me of a recent StackOverflow blog saying the following: "It is a good idea to guide the newbie to arrive at a good question, and let them know what they don't know that they don't know. / to continue, ...

@Matthew, / continued, ... It is only when the newbie sees the big picture, knows the basic things that he should know, and then uses a hobbyist friendly language to ask the question, then other newbies, ninjas, and pros can all join in to contribute a newbie language.

@Matthew, / continue, ... When I first read your question, I was surprised of two things: (1) How come this guy presents his question so succinctly and effectively, (using eye catching little yellow cubes etc), (2) But at the same time, this guy is using electronics amateurish language (eg, "transistor chips" instead of "transistor", "servo motor" instead of, in short, "servo" which we hobbyists always use). / to continue, ...

@Matthew / to continue, ... One of my hobbies is "technical presentation" and "effective communication", so before I start answering any question, I almost always check the asker's profile, to make sure we are talking the same "language". When I skimmed your profile, I was surprised of another two things: (3) Your educational and career background, (4) Your long history with EESE and your very short list of questions and answers here. My surprise #3 of course make Surprises #1, #2 no longer surprising. / to continue, ...

@Matthew /continued, ... And before I make an answer, I sometimes also let the asker know myself, a little bit more than my short profile in this EE SE. (1) I also have a MSc IT, at Imperial College London. I also once studies, (but dropped out after a year), in the Cybernetics Dept in Reading (UK's Reading. :)) (2) It is only two years ago that I bought my first toy servo. I am a poor hobbyist, and I never played any RC toys, not to mention drones. / to continue, ...

@Matthew / continue, ...The price of drones dropped so very much these years, that it has become a popular toy, and I would lose face if my 10 year old niece discovers that I don't know nothing about drones. I know that drones use servos, but also BLDC (BrushLess DC) motors, which is another thing I don't know nothing about (I do know toy DC motors very well, though).

@Matthew, /continued, ... (3) Now, my 3 year hobbyist learning and project plan: Make a cyber cat using 4 servos (You can find more details about my cyber cat project in the chat room chatting here: chat.stackexchange.com/rooms/112589/… ).

@Matthew. / continue, ...I will stop my TLDR pre-answer introduction here. You might like to tell me your learning/project plan, so that I can tailor my answer to fit the plan of yours and other future newbies. Cheers.

@tlfong01 I really appreciate your kind of approach and the very complete and documented hobbyst's oriented answers that you write. I got to note that yellow duck from HK, since that remarkable answer when you told us about your struggle for hacking with GPS devices from home.

@tlfong01 provided this reference RpiZero Power Supply through 40 pin Power/GPIO Header or microUSB connector. || Note the warnings from Chris and in my answer.

@RussellMcMahon Thank you for your help. I think it is a very good idea to open a chat room to clarify the user's requirements and skills before me starting an answer. Actually I hope to know if the OP has a multi-meter and a bread board, and knows the basic techniques of soldering.

@RussellMcMahon @mguima Actually just now I tried to open a chat room and invite everybody to discuss things. However I could not find any option to open a chat room. I know other users with higher reputation points can do that. I prefer to first draft an answer, casually upload pictures and programs in the chat room, so everybody can comment or make counter suggestions, to make sure I have not misunderstood the OP's question. This is what I will be doing now in this chat room. Cheers.

@RussellMcMahon Thank your for reminding me about the warnings when giving my answer. I will read them to see if I need to pay attention on something I am missing. I hope my to complete answer will no longer induce any warnings. Cheers.

@mguima Thank you very much for your nice words and encouragement. One reason that my answers are newbie friendly is that (1) I studied an EE diploma in a community college where, unlike universities, our teachers and text books used a language that "ordinary people" can easily understand. Later I also taught in a community college where I enjoyed telling the much disadvantaged, low privileged mature students / to continue, ...

about Ohm's Law, how to blink a LED, and even NE555 timer, which gave them great joy and a big sense of achievement which they unfairly got so little in their real hard life, working 8 days a week, like a dog, youtube.com/watch?v=0fFyZzqPDws. Cheers.

Wow, thanks all for the discussion. I am into electronics as a hobby. I have studied software engineering, but the not familiar with too much electrical engineering. I am trying to design an automatic dog feeder... I want to plug in the device once, then power the raspberry pi and a 12 V dc motor.

Batteries are not an option... I believe there should be a way that I can integrate the R. PI with the motors. The motor is a 12 V one which will be controlled by that motor control chip.