Hello Christophe

> Can convert my (old PSU1) powersupply to 110V, or should I buy a new PSU and install that

If you think you can obey the warning: "The following notes are intended
for experts onyl. Carrying out of works described in these documents is
allowed only for authorized personnel who are familiar with all valid
safety rules" and are able to solder and handle a screwdriver, then get
the description here:
http://www.doepfer.de/faq/a100_faq.htm#Modification%20mains%20voltage


If not: any electronic repair service will do it within 30 minutes of
work (disassembling and assembling the housing is the main effort).

Florian