Less noisy version of max232
RS232 signals swing both 12V positive and negative.  You can sometimes get away with swinging from positive to ground, without a negative level, but (a) it’s not standards compliant and (b) you can’t count on It working. 

Hence the value of the MAX232, which provides its own supplies for that swing. 

If it’s putting too much noise on the power rail, you should fix that problem instead of trying to reinvent a chip that’s worked well in lots of designs. 

A brute force approach is a completely separate supply to regulate the power to the MAX232. Either a linear regulator or DC-to-DC regulator would do it.  

Short of that, some low ESR capacitors and ferrites could be tried.