From: Ken Seefried <ken(a)seefried.com> digital First switch mode vs linear only covers HOW the regulation is obtained in a power supply unit. Most of the DEC PDP-11s had switch mode supplies especially the Qbus PDP-11s though many of the later Unibus systems did as well. The problem using a PC supply is that DEC supplies provide DCok and BeventL (line time clock) to name a few signals plus the +12 and -12 power may exceed most PC PSUs. the later is something for a case by case study. I have used a 200W PC supply (it was handy) to run a 12 slot H9281-AC with 10 cards in it. I had to supply DCok and Bevent-L, it was otherwise ok. Allison