In regards to this supply, I am fairly sure that there is a positive and negative side to the logic supply voltage. If he is a LM 317, I can almost be positive that he will have a similar component that is dealing with the negative side as well as the positive side. Since most of the IC Components will need +15 to 30VDC and -15V to 30V Dc in order for the IC's to regulate the PWM (Pulse Width Modulation)of the supply since most supplies run either an SCR or a IGBT to produce the amount of power his supply is requiring. 300W is a good amount of power. I am used to dealing with 4 to 18kW but the effect is very much the same. You have your 208 comming in, you have your rectification, you have an input cap which stores your current and a device such as an IGBT or an SCR that will switch the current and charge at a specified rate out through a filter choke and into an output capacitor. The switching is regulated usually by a CMos based chip with either a single or dual drive gate pulse which will either be inverted and cleaned up through a gate drive, and then be pushed into the IGBT or SCR Drive through a Snubber Circuit.
Now if you have an LM317 Your limit for the supplied AC Comming into the circuit will be 40V of the half cycle so if you have 62.5V AC On the input terminal you need to look at your true RMs of 44VDC give or take a few hundred millivolts. Now if this supply is how you bought it, then your problem is that you may have shorted a winding in your secondary giving you more voltage than you need. So you may want to check that the impedance of the secondary is up to spec. Traditionally, if you lose part of the winding, it will being to put out more voltage than it is specified for.
Now I would look to see that your Primary has the correct voltage and that the secondary is also putting out what the transformer is rated for. If it is over that, then you will need to replace it. Mind you, your reading will be different from loaded and unloaded.