I've came across this claim a couple of times, but I really seem not to find any references or sources that would look legitimate.
Only thing I have found obscure internet sites with very political leftist tint. While it doesn't make me to outright dismiss them as conspiracy theories par excellence, the sources are such that I'd would like to find some other confirmation.
Only other thing I know about is an episode in British TV drama series Foyle's War that referenced this, but that at most proves that writers of series have also heard stories about this kind of profiteering and were inspired enough to write an episode.
For example, contrast with the IBM subsidiary or such that sold some equipment to Nazis, which is at least somewhat documented.
"Allied" companies were doing a lot of business in Germany before the war - indeed the largest German truck manufacturer (Opel) was a subsidiary of General Motors. It speaks to the very internationalized nature of business and corporations even in this era.
I would however pretty much ignore sensationalist claims that Allied companies supplied the Germans during the war. It just wasn't going get through the blockade. Indeed, the IBM sale of equipment to the Nazis occurred in 1933 - which is why the book accusing IBM of "helping" the Holocaust is just being very silly.