My "go-to" fits-everything connecting method was pink Hellermann sleeves.
When dealing with gear that had one of the multifarious variety of 2-pin chassis-mounted plugs for its power-input I'd pop a suitably-sized Hellermann over each pin, then push the tinned end of a flex-core in so it ran alongside the pin and was kept pressed against it by the elasticity of the sleeve.
[In times-past it was quite common for 'communications' equipment to arrive back at the lab without its associated mains-lead - this usually being wired into a FCU or similar semi-permanent outlet to deter casual umplugging/switching-off-at-the-mains, or alternatively the mains-lead would be securely cable-tied into the rest of the cables round the back of the rack and a pig's-ear to remove without disturbing other stuff. You therefore had to make-do however you could in order to power-up the equipment in the absence of its official cable].
There was _just_ enough room to do the Hellermann trick with a 6-pin 'small' Bulgin connector - I came across quite a few 48V power-units that used these connectors. Why 6-pin, you ask? Well, the supplies had internally a SMPS and were designed to be fed from either 240VAC or 12VDC - either could be fed in through the Bulgin depending on which pins you used. On one occasion my Hellermann trick managed to feed 240VAC into the 12VDC pins
