I cannot cite any specific examples of retributive acts by Jews against Germans being either condoned or encouraged by the western Allied powers, but one could make the argument that the policies behind the Allied occupation were intrinsically retributive. The policy debate between retribution and reconstruction was hotly debated in the White House, for example. Henry Morgenthau, the Secretary of the Treasury, was particularly drawn to the idea that Allied economic policy should be geared towards "de-industrializing" the German state such that it would be transformed into a "pastoral" nation with a smaller population density and its economy primarily driven by agriculture. JCS 1067 - often called the Morgenthau Plan - contains the blueprint of this perspective in action. Section four details the basic goals of the occupation (this perspective would rapidly change, however, in the first years of the occupation and the transition to the Truman administration as I will detail later):

"4. Basic Objectives of Military Government in Germany:

a. It should be brought home to the Germans that Germany's ruthless warfare and the fanatical Nazi resistance have destroyed the German economy and made chaos and suffering inevitable and that the Germans cannot escape responsibility for what they have brought upon themselves.

b. Germany will not be occupied for the purpose of liberation but as a defeated enemy nation. Your aim is not oppression but to occupy Germany for the purpose of realizing certain important Allied objectives. In the conduct of your occupation and administration you should be just but firm and aloof. You will strongly discourage fraternization with the German officials and population.

c. The principal Allied objective is to prevent Germany from ever again becoming a threat to the peace of the world. Essential steps in the accomplishment of this objective are the elimination of Nazism and militarism in all their forms, the immediate apprehension of war criminals for punishment, the industrial disarmament and demilitarization of Germany, with continuing control over Germany's capacity to make war, and the preparation for an eventual reconstruction of German political life on a democratic basis.

d. Other Allied objectives are to enforce the program of reparations and restitution, to provide relief for the benefit of countries devastated by Nazi aggression, and to ensure that prisoners of war and displaced persons of the United Nations are cared for and repatriated."

Here is a link to the full text of JCS 1067: http://en.wikisource.org/wiki/JCS_1067

The retributive perspective in JCS 1067 was also preferred by the Soviet Union - the nation that had launched two invasions into its sovereign territory in living memory (into the Russian Empire in WWI and the USSR in WWII) needed to be permanently disarmed by having its industrial capacity "appropriated" and sent to the victim-nations of Nazi aggression as a form of war reparation. During their brief seat at the table in Allied-occupied Germany, the French also maintained a strongly retributive stance on the occupation.

Here is a different discussion thread in which I detail and source Allied economic policy in regards to food rationing. It is arguable that the extremely low caloric standards for German civilian food rationing was both a practical necessity - since global food supplies were low due to the ravages of war - but also because the Allies favored larger food rations for the citizens of nations that had been occupied by Germany rather than an equitable distribution amongst all Europeans.

As a mentioned earlier, however, the western Allies - especially the Americans and the British - underwent a shift in their occupation policies. Explaining how and why Washington changed its stance is still hotly debated in the field. Many books have been written trying to determine whether or not Roosevelt truly believed in a retributive policy - the kind favored by the USSR and the French. Some scholars argue that he had planned all along to reindustrialize Germany instead of deindustrializing it. Others argue that he planned to stick with his agreements with Stalin to see Germany reduced to a pastoral nation.

Whatever the case, he died before his long term plans (whatever they may have been) could be actualized. All we are left with are the policies of the immediate occupation, which were definitely retributive.

With the death of FDR, Harry S. Truman took over the White House and brought with him different policy advisers and cabinet members. Holdovers from the Roosevelt Administration, such as Morgenthau, quickly left the administration as they found themselves suddenly in the minority when it came to the retribution-rebuilding debate. Both administrations had people who favored either perspective, but Truman's administration took a decisive turn in favor of rebuilding Germany. Some historians argue that Truman favored rebuilding Germany as a means to foster an industrial ally in the fight against the Soviet Union. Others argue that the US-Soviet split and the beginning of the Cold War didn't truly begin until Truman reneged on the post-war agreements made at the Yalta convention (between FDR and Stalin). These agreements included keeping Germany as one unified nation run by one unified government along with the commitment to destroy Germany's industrial capacity.

What is fairly clear is that many who argued against retributive policies did so because they believed it would be economically disastrous to the already-weakened global economy, international politics aside. The free flow of goods being produced by industrial nations had become the modus operandi for the mid-20th century economy, and the Allied nations needed an industrially powerful Germany in order to play its part in that global economic nexus.

A great source which provides an excellent overview of this subject is Carolyn Eisenberg's Drawing the Line: The American Decision to Divide Germany.

Many of the judges in the Nurenberg trials were Jewish.