This particular exchange was reportedly between Erwin Rommel and Luftwaffe chief Hermann Göring in September 1942. The British military historian B. H. Liddell-Hart popularized this interlude in his book The Rommel Papers published in 1953. These were a translated and collected series of letters and reminiscences that helped build up the postwar mythos of the Field Marshal. This particular section came from Krieg ohne Haß (War without Hatred), which is a curious posthumous 1950 memoir of Rommel's published in postwar Germany by DAK staff officer Fritz Bayerlein with the assistance of Rommel's wife. The passage is as follows:

During the conference I realised that the atmosphere in the Fuehrer's H.Q. was extremely optimistic. Goering in particular was inclined to minimise our difficulties. When I said that British fighter-bombers {which Rommel had claimed were using American war materials} had shot up my tanks with 40-mm shells, the Reichsmarschall, who felt himself touched by this, said: "That's completely impossible. The Americans only know how to make razor blades." I replied: "We could do with some of those razor blades, Herr Reichsmarschall."

This particular quote gained a good deal of currency in the postwar period, especially in the Anglosphere as it painted Rommel, and the German officer corps by extension, as appreciative of America's industrial might while Hitler and his cronies were dismissive of their enemy.

But it bears mentioning that there is not much corroborating this exchange. Bayerlein was part of a larger trend of German generals postwar that sought to explain and excuse their lost war. This included the earliest iterations of what historians now term "the clean Wehrmacht myth" in which only a criminal few Nazis were guilty of crimes while the military fought an honorable war. Rommel was part of this postwar cleansing of the historical record as he fought in theaters that were allegedly free of mass war crimes and his tangential involvement in the 20 July Plot set him against Hitler. Liddell-Hart was a collaborator of sorts with these German generals as the British historian and theorist was also a supporter of West German rearmament. He argued that German generals were "technicians" who were above politics like good soldiers.

The above is one of the reasons why historians in 2018 are very skeptical of these types of insider sketches of the German war effort. Men like Bayerlein had every incentive to embellish their acumen and insight while throwing as much shade as possible at Nazi figures like Göring. The exchange itself may have occurred as Krieg ohne Haß outlined, but it bears stressing that a good many sources from the period (i.e. ones not produced in the postwar) show that Göring's attitude was all too typical among the Wehrmacht's officers. There was a widespread dismissal within interwar German culture that painted America as the land of shoddy, mass-produced merchandise which stood in stark contrast to German craftsmanship. Hitler and other Nazi leaders may have dismissed American industrial might, but they were far from alone in that.

Sources

Major, Patrick. "‘Our Friend Rommel’: The Wehrmacht as ‘Worthy Enemy’ in Postwar British Popular Culture." German History 26, no. 4 (2008): 520-535.

Weinberg, Gerhard L. "Hitler's image of the United States." The American Historical Review 69, no. 4 (1964): 1006-1021.