From the Guidelines

50mg tramadol is weaker than 5mg oxycodone.

The conversion factor for tramadol is 0.2, and for oxycodone is 1.5, as shown in the CDC clinical practice guideline for prescribing opioids for pain 1.
This means that 50mg of tramadol is equivalent to 10mg of morphine (50mg x 0.2), while 5mg of oxycodone is equivalent to 7.5mg of morphine (5mg x 1.5).
Although the morphine equivalent dose of 50mg tramadol is higher than that of 5mg oxycodone, tramadol is considered a weaker opioid due to its dual mechanism of action, which includes inhibition of norepinephrine and serotonin reuptake, in addition to its weak mu-opioid receptor agonist activity 1.
The NCCN panel recommends a maximum daily dose of 400mg for tramadol, and notes that it is less potent than other opioids, approximately one-tenth as potent as morphine 1.
In contrast, oxycodone is a stronger opioid with a higher potential for abuse and dependence, and is typically used for moderate to severe pain 1.
Overall, while the morphine equivalent dose of 50mg tramadol may be higher than that of 5mg oxycodone, tramadol is generally considered a weaker opioid due to its unique mechanism of action and lower potency compared to other opioids like oxycodone.

From the Research

The study 2 compared the analgesic efficacy of oxycodone and tramadol in an emergency unit, and found that oxycodone is not inferior to tramadol in terms of analgesia.
Another study 3 compared the analgesic efficacy of tramadol 100 mg, tramadol 50 mg, codeine 60 mg, aspirin with codeine, and placebo, and found that tramadol 100 mg was statistically superior to placebo for some measures of efficacy, while tramadol 50 mg was only statistically superior to placebo for remedication time.
A study 4 compared the analgesic efficacy of 50 and 100 mg oral tramadol with a standard analgesic (1000 mg paracetamol + 60 mg codeine) and placebo after orthopaedic surgery, and found that the standard analgesic was significantly superior to both 50 mg tramadol and 100 mg tramadol.

The study 3 used doses of tramadol 100 mg and tramadol 50 mg, and found that the 100 mg dose was more effective than the 50 mg dose.
The study 4 used doses of 50 and 100 mg oral tramadol, and found that neither dose was effective in providing analgesia after orthopaedic surgery.
There is no direct comparison of 50mg tramadol and 5mg oxycodone in the provided studies, but the study 2 suggests that oxycodone and tramadol are equivalent in terms of analgesia, and the study 3 suggests that tramadol 50 mg may not be as effective as other analgesics.

Tramadol's mechanism of action involves both opioid and monoaminergic activity, as described in the study 5.
Oxycodone's mechanism of action is not explicitly described in the provided studies, but it is known to be an opioid agonist.
The study 6 found that single-dose tramadol did not impair oxycodone clearance, suggesting that the two drugs do not interact significantly in terms of metabolism.