Need to Determine Power Cable For Old Bose Found In Basement
120V 50/60hz 350W Max


This means that you can plug it directly into the wall, assuming you live in a country where the mains voltage is 120V (US, Canada, and others). 50/60Hz tells you that it will work with both 50Hz and 60Hz mains voltage, and the 350W tells you that it will draw a maximum of 350W, which means that at a nominal 120V, it will draw a maximum of 3 Amps.

That connector is tricky, however. It doesn't appear to be a standard IEC inlet. However, I suspect it will fit an nonstandard variant of an IEC C7 plug (sometimes designated "C7P" for "polarized"):



This plug is used by Bose on other equipment, and is somewhat common on consumer audio equipment. I'm not sure why the inlet on your amplifier doesn't have the bulges on the side, but in any case, it should be possible to safely use a connector of the type linked above. To verify that this connector will work, measure the pitch of the pins on that inlet. The C7 and C7 variant plug have a pin spacing of 8.6mm, center to center.