Intermittently - car cranks but but does not start. On the way to work in the morning - got off the highway & came to a stop and car died. Started right up after about 5 minutes.

So far -

New battery
Checked for codes - none
No warning on display

Ran a/c diagnostic and 24 showed only rose to 10.5 when car wouldnt start. Rose to 13.5 when running. Dropped to 13 when all accessories running.

Belt feels tight no cracks. Hear humming from rear of engine when key is in position 2.

Thinking either...

CPS
Voltage Regulator
Alternator

How do I know which one is the culprit?

If the engine dies and turns over but won't start, then I would first suspect the CPS.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

CPS

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

I'd go with the crank position sensor. Sometimes they wont set a code. Many bad ones I've dealt with need more than 5 minutes to cool off. 30 minutes to an hour is what I'm accustomed to seeing. If the car dies, then spins over but wont start, and then you spray water on it and the engine starts, you found the problem for sure.

Is there any way to be 100% sure without taking the alternator out or taking it to the stealer?

Reason I ask is because I dont read over 13.5 when engine is running using ac diagnostic...

http://www.ehow.com/how_4601849_verify-alternator-working.html

Also - I disconnected negative battery terminal while engine was running and engine didnt die.

http://www.ehow.com/how_4519042_check-vehicle-alternator.html

These facts seem to contradict each other to me.