Because partir is not really relevant here, it's the conditionnel passé of devoir, which is not a "house" verb, and so always uses avoir.  It doesn't matter what kind of verb comes afterwards.

Thank you Alan

Thank you !

But does « je devrais allé ‘ (using past participle of aller) mean the same thing as « j’aurais dû aller » ?

Hi Cécile,

Candy is specifically asking about "je devrais allé". I know this just seems like a spelling error, and probably it is, but if you google this (and similar constructions like "je devrais acheté") you get a surprising number of results. Actually there are more results for "je devrais allé" (162) than for "je devrais aller" (61). (By the way, when doing a search like this on Google, the initial number of results is not correct, it's always too large. To get the correct number you need to page through the results until you get to the last one.)

Do you think this is a common spelling error in French, or is there some other reason?

Thank you, Alan! Nope, it’s not a spelling error. I just need a native speaker to tell me if “ je devrais allé” is ever acceptable because some online translation tools say yes. 

Candy

Hi Candy, I didn't mean that you had made a spelling error - obviously this is what you intended - but the hits on Google look like errors to me. (But maybe it's some dialect thing?) 

It's true that Google Translate, for example, will translate "Je devrais allé" as "I should have gone", but it will always attempt to give an answer, even if the input is incorrect. If you do the translation in the opposite direction it gives "j'aurais dû aller" instead.

Have you seen examples of "je devrais allé" in print? Or have you heard people saying this?

Merci beaucoup !!

I have heard someone say it, but it was not a native speaker. So I looked it up online and thought, hmmm, maybe ?  Thank you very much for your help and thank you Cécile !

Hi Aurélie,

The other day I found myself trying to say (verbally), by starting off 'Je devrais..', e.g. "I should do..", and stalling, having wanted to turn it into "I should have done" - I was probably doing along the lines of what the 6 May 2018 poster was thinking ('I must have had to..' rather than 'I would have had..').I think this lesson and your above response explains it.

To get the stupid question out of the way, there's no way 'Je devrais avoir eu' makes any sense, is there? (I'm guessing I was trying to construct the conditional past by combining conditional present and pluperfect).

Thanks!

Tom