Hi! I am an international student from Romania and I want to apply to universities in the USA, but also in the UK. I found out that IELTS is accepted in both of them, so I was thinking about taking IELTS instead of taking two language tests (Cambridge and TOEFL).
Is it going to afect me in any way considering that most international students who apply in the US take TOEFL?
nope, but some schools don’t accept IELTS (US).
I think you are better off taking TOEFL. As the above post says, not all universities accept IELTS but all of them accept TOEFL 
Most colleges and universities in the US will accept IELTS. Check the websites of the places that you are interested in to find out their specific requirements.
The counselors at the EducationUSA office in Bucharest should be able to help you with this. Contact them https://educationusa.state.gov/centers/fulbright-bucharest